Web App Questionnaires in ASP.NET Web Forms

I searched and could not find the correct term to correct my mistake. I created an AppWeb where the user chooses a subject in a DropDownList and it loads a questionnaire from the database. What happens is that if there is simultaneous access several different errors occur:

I have verified in the browser that the request is correct (Params) but the Response sends the page according to the previous parameters.

Apparentlyitisnotacceptingmorethanoneusertodothequestionnaire,andtheservercachesthefirstchoiceanddoesnotupdatethepageevenwithanewparameter.Ihopeyouhaveunderstoodandthatyoucanhelpme.Aspxcode:

<asp:ContentID="BodyContent" ContentPlaceHolderID="MainContent" runat="server">
    <style type="text/css">
    .modalPopup
    {
    background-color: #fffddd;
    padding: 3px;
    z-index: 10001;
    }
    </style>
    <div class="panel panel-default">
        <div id="divtest" runat="server">
             <asp:Label ID="label" runat="server" Text="Escolha uma disciplina abaixo:"></asp:Label>

             <asp:DropDownList ID="DropDownList1" runat="server" AutoPostBack="true" CssClass="dropdown form-control" OnSelectedIndexChanged="btnCarregarClick">
                                    <asp:ListItem Enabled="false">Português</asp:ListItem>
                                    <asp:ListItem >Racíocinio</asp:ListItem>
                                    <asp:ListItem Enabled="false">História</asp:ListItem>
                                    <asp:ListItem Enabled="false">Geografia</asp:ListItem>
                                    <asp:ListItem >Direito Constitucional</asp:ListItem>
                                    <asp:ListItem >Outros Direitos</asp:ListItem>
                                </asp:DropDownList>

            <asp:Button ID="btnCarregar" runat="server" Text="Carregar" CssClass ="btn btn-primary" OnClick="btnCarregarClick"/>
        </div>
            <div class ="panel-body col-md-12">
                <asp:Panel ID="UpdPanel" runat="server">

                    <table id="tbl">
                        <tr>
                        <asp:Label ID="Label1" runat="server" Text="Label" Visible="false"></asp:Label>      
                            <asp:RadioButtonList ID="RadioButtonList1" runat="server" OnSelectedIndexChanged="rdbList1_SelectedIndexChanged"></asp:RadioButtonList>
                        </tr><tr>
                        <asp:Label ID="Label2" runat="server" Text="Label" Visible="false"></asp:Label>
                            <asp:RadioButtonList ID="RadioButtonList2" runat="server" OnSelectedIndexChanged="rdbList2_SelectedIndexChanged"></asp:RadioButtonList></tr><tr>
                        <asp:Label ID="Label3" runat="server" Text="Label" Visible="false"></asp:Label>
                            <asp:RadioButtonList ID="RadioButtonList3" runat="server" OnSelectedIndexChanged="rdbList3_SelectedIndexChanged"></asp:RadioButtonList></tr><tr>
                        <asp:Label ID="Label4" runat="server" Text="Label" Visible="false"></asp:Label>
                            <asp:RadioButtonList ID="RadioButtonList4" runat="server" OnSelectedIndexChanged="rdbList4_SelectedIndexChanged"></asp:RadioButtonList></tr><tr>
                        <asp:Label ID="Label5" runat="server" Text="Label" Visible="false"></asp:Label>
                            <asp:RadioButtonList ID="RadioButtonList5" runat="server" OnSelectedIndexChanged="rdbList5_SelectedIndexChanged"></asp:RadioButtonList></tr><tr>
                        <asp:Label ID="Label6" runat="server" Text="Label" Visible="false"></asp:Label>
                            <asp:RadioButtonList ID="RadioButtonList6" runat="server" OnSelectedIndexChanged="rdbList6_SelectedIndexChanged"></asp:RadioButtonList></tr><tr>
                        <asp:Label ID="Label7" runat="server" Text="Label" Visible="false"></asp:Label>
                            <asp:RadioButtonList ID="RadioButtonList7" runat="server" OnSelectedIndexChanged="rdbList7_SelectedIndexChanged"></asp:RadioButtonList></tr><tr>
                        <asp:Label ID="Label8" runat="server" Text="Label" Visible="false"></asp:Label>
                            <asp:RadioButtonList ID="RadioButtonList8" runat="server" OnSelectedIndexChanged="rdbList8_SelectedIndexChanged"></asp:RadioButtonList></tr><tr>
                        <asp:Label ID="Label9" runat="server" Text="Label" Visible="false"></asp:Label>
                            <asp:RadioButtonList ID="RadioButtonList9" runat="server" OnSelectedIndexChanged="rdbList9_SelectedIndexChanged"></asp:RadioButtonList></tr><tr>
                        <asp:Label ID="Label10" runat="server" Text="Label" Visible="false"></asp:Label>      
                            <asp:RadioButtonList ID="RadioButtonList10" runat="server" OnSelectedIndexChanged="rdbList10_SelectedIndexChanged"></asp:RadioButtonList></tr>

                    </table>
                </asp:Panel>  
                    <asp:Button Visible="false" ID="btnCorrigir" runat="server" Text="Corrigir" CssClass ="btn btn-primary" OnClick="btnCorrigir_Click"/>
                    <asp:Label ID="lbll" Visible="false" Style="font-size:x-large" runat="server"></asp:Label>
                    <asp:Label ID="lblll" Visible="false" runat="server">Clique em gabarito para vê-lo.</asp:Label>
                    <asp:Button ID="btnok" CssClass="btn btn-primary" Visible="false" runat="server" Text="Gabarito" OnClick="btnok_click" />
                    <asp:LinkButton ID="Linkbtn" CssClass="btn btn-danger" Visible="false" runat="server" Text="Voltar" PostBackUrl="~/Default.aspx" />
                    <div ID="div" runat="server" visible="False">     
                        <asp:Panel ID="Panel1" runat="server" CssClass="modalPopup" Style="display: table" >
                            <table style="width: 270px">
                            <tr>
                            <td>
                                <asp:Label ID="lblGabarito" runat="server" Height="30px" Text="Gabarito"></asp:Label>
                            </td>
                            </tr>
                            <tr>
                            <td style="width: 30% ">
                                <asp:Label ID="lblPergunta1" runat="server" Height="30px"></asp:Label>
                                <asp:Label ID="lblPergunta2" runat="server" Height="30px"></asp:Label>
                                <asp:Label ID="lblPergunta3" runat="server" Height="30px"></asp:Label>
                                <asp:Label ID="lblPergunta4" runat="server" Height="30px"></asp:Label>
                                <asp:Label ID="lblPergunta5" runat="server" Height="30px"></asp:Label>
                                <asp:Label ID="lblPergunta6" runat="server" Height="30px"></asp:Label>
                                <asp:Label ID="lblPergunta7" runat="server" Height="30px"></asp:Label>
                                <asp:Label ID="lblPergunta8" runat="server" Height="30px"></asp:Label>
                                <asp:Label ID="lblPergunta9" runat="server" Height="30px"></asp:Label>
                                <asp:Label ID="lblPergunta10" runat="server" Height="30px"></asp:Label>
                            </td>  
                            </tr>
                            <tr>
                            <td >
                            </td>
                            <td> &nbsp; &nbsp; &nbsp;
                                <asp:Button ID="btnT" CssClass="btn btn-xs" runat="server" Text="Encerrar" /></td>
                            </tr>
                            </table>
                            </asp:Panel> 
                    </div>
                    <asp:ModalPopupExtender ID="ModalPopupExtenderLogin" runat="server"
                        TargetControlID="btnok"
                        PopupControlID="Panel1"
                        BackgroundCssClass="modalBackground"
                        DropShadow="true"
                        CancelControlID="btnT" /> 

            </div>    
    </div>
</asp:Content>

C # code:

 namespace dygaquiz
{
    public partial class Questionario : System.Web.UI.Page
    {
        int count, rbl1, rbl2, rbl3, rbl4, rbl5, rbl6, rbl7, rbl8, rbl9, rbl10;
        Crud crud = new Crud();
        static List<QuestionarioDados> questio = new List<QuestionarioDados>();
        public class QuestionarioDados
        {
            public int Id { get; set; }
            public string Pergunta { get; set; }
            public int certa { get; set; }
            public DataSet Ds { get; set; }
        }
        protected void Page_Load(object sender, EventArgs e)
        {

        }
        protected void btnok_click(object sender, EventArgs e)
        {
            ModalPopupExtenderLogin.Show();
        }
        protected void btnCarregarClick(object sender, EventArgs e)
        {

            CarregarQuestionario(DropDownList1.SelectedIndex);
            div.Visible = true;

        }
        protected void btnCorrigir_Click(object sender, EventArgs e)
        {
            count = 0;
            Corrigir();
            btnCorrigir.Visible = false;
        }
        public void Corrigir()
        {

            if (RadioButtonList1.SelectedItem != null)
            {
                if (questio[0].certa.ToString() == rbl1.ToString())
                {
                    RadioButtonList1.SelectedItem.Attributes.Add("style", "background-color:green");
                    count++;
                }
                else
                {
                    RadioButtonList1.SelectedItem.Attributes.Add("style", "background-color:red");

                }
            }
            if (RadioButtonList2.SelectedItem != null)
            {
                if (questio[1].certa.ToString() == rbl2.ToString())
                {
                    RadioButtonList2.SelectedItem.Attributes.Add("style", "background-color:green");
                    count++;
                }
                else
                {
                    RadioButtonList2.SelectedItem.Attributes.Add("style", "background-color:red");

                }
            }
            if (RadioButtonList3.SelectedItem != null)
            {
                if (questio[2].certa.ToString() == rbl3.ToString())
                {
                    RadioButtonList3.SelectedItem.Attributes.Add("style", "background-color:green");
                    count++;
                }
                else
                {
                    RadioButtonList3.SelectedItem.Attributes.Add("style", "background-color:red");

                }
            }
            if (RadioButtonList4.SelectedItem != null)
            {
                if (questio[3].certa.ToString() == rbl4.ToString())
                {
                    RadioButtonList4.SelectedItem.Attributes.Add("style", "background-color:green");
                    count++;
                }
                else
                {
                    RadioButtonList4.SelectedItem.Attributes.Add("style", "background-color:red");

                }
            }
            if (RadioButtonList5.SelectedItem != null)
            {
                if (questio[4].certa.ToString() == rbl5.ToString())
                {
                    RadioButtonList5.SelectedItem.Attributes.Add("style", "background-color:green");
                    count++;
                }
                else
                {
                    RadioButtonList5.SelectedItem.Attributes.Add("style", "background-color:red");

                }
            }
            if (RadioButtonList6.SelectedItem != null)
            {
                if (questio[5].certa.ToString() == rbl6.ToString())
                {
                    RadioButtonList6.SelectedItem.Attributes.Add("style", "background-color:green");
                    count++;
                }
                else
                {
                    RadioButtonList6.SelectedItem.Attributes.Add("style", "background-color:red");

                }
            }
            if (RadioButtonList7.SelectedItem != null)
            {
                if (questio[6].certa.ToString() == rbl7.ToString())
                {
                    RadioButtonList7.SelectedItem.Attributes.Add("style", "background-color:green");
                    count++;
                }
                else
                {
                    RadioButtonList7.SelectedItem.Attributes.Add("style", "background-color:red");

                }
            }
            if (RadioButtonList8.SelectedItem != null)
            {
                if (questio[7].certa.ToString() == rbl8.ToString())
                {
                    RadioButtonList8.SelectedItem.Attributes.Add("style", "background-color:green");
                    count++;
                }
                else
                {
                    RadioButtonList8.SelectedItem.Attributes.Add("style", "background-color:red");

                }
            }
            if (RadioButtonList9.SelectedItem != null)
            {
                if (questio[8].certa.ToString() == rbl9.ToString())
                {
                    RadioButtonList9.SelectedItem.Attributes.Add("style", "background-color:green");
                    count++;
                }
                else
                {
                    RadioButtonList9.SelectedItem.Attributes.Add("style", "background-color:red");

                }
            }
            if (RadioButtonList10.SelectedItem != null)
            {
                if (questio[9].certa.ToString() == rbl10.ToString())
                {
                    RadioButtonList10.SelectedItem.Attributes.Add("style", "background-color:green");
                    count++;
                }
                else
                {
                    RadioButtonList10.SelectedItem.Attributes.Add("style", "background-color:red");

                }
            }
            if (count == 1)
            {
                lbll.Text = "Acertou " + count.ToString() + " questão.";
            }
            if (count == 0)
            {
                lbll.Text = "Não acertou questão alguma.";
            }
            if (count > 1)
            {
                lbll.Text = "Acertou " + count.ToString() + " questões.";
            }
            btnCorrigir.Visible = false;
            btnok.Visible = true;
            Linkbtn.Visible = true;
            lblll.Visible = true;
            lblPergunta1.Text = "Questão 1: " + ((int)questio[0].certa + 1);
            lblPergunta2.Text = "Questão 2: " + ((int)questio[1].certa + 1);
            lblPergunta3.Text = "Questão 3: " + ((int)questio[2].certa + 1);
            lblPergunta4.Text = "Questão 4: " + ((int)questio[3].certa + 1);
            lblPergunta5.Text = "Questão 5: " + ((int)questio[4].certa + 1);
            lblPergunta6.Text = "Questão 6: " + ((int)questio[5].certa + 1);
            lblPergunta7.Text = "Questão 7: " + ((int)questio[6].certa + 1);
            lblPergunta8.Text = "Questão 8: " + ((int)questio[7].certa + 1);
            lblPergunta9.Text = "Questão 9: " + ((int)questio[8].certa + 1);
            lblPergunta10.Text = "Questão 10: " + ((int)questio[9].certa + 1);
            questio.Clear();
        }
        protected void rdbList1_SelectedIndexChanged(object sender, EventArgs e)
        {

            rbl1 = RadioButtonList1.SelectedIndex;
        }
        protected void rdbList2_SelectedIndexChanged(object sender, EventArgs e)
        {
            //pega o index da lista de radio
            rbl2 = RadioButtonList2.SelectedIndex;
        }
        protected void rdbList3_SelectedIndexChanged(object sender, EventArgs e)
        {
            //pega o index da lista de radio
            rbl3 = RadioButtonList3.SelectedIndex;
        }
        protected void rdbList4_SelectedIndexChanged(object sender, EventArgs e)
        {
            //pega o index da lista de radio
            rbl4 = RadioButtonList4.SelectedIndex;
        }
        protected void rdbList5_SelectedIndexChanged(object sender, EventArgs e)
        {
            //pega o index da lista de radio
            rbl5 = RadioButtonList5.SelectedIndex;
        }
        protected void rdbList6_SelectedIndexChanged(object sender, EventArgs e)
        {
            //pega o index da lista de radio
            rbl6 = RadioButtonList6.SelectedIndex;
        }
        protected void rdbList7_SelectedIndexChanged(object sender, EventArgs e)
        {
            //pega o index da lista de radio
            rbl7 = RadioButtonList7.SelectedIndex;
        }
        protected void rdbList8_SelectedIndexChanged(object sender, EventArgs e)
        {
            //pega o index da lista de radio
            rbl8 = RadioButtonList8.SelectedIndex;
        }
        protected void rdbList9_SelectedIndexChanged(object sender, EventArgs e)
        {
            //pega o index da lista de radio
            rbl9 = RadioButtonList9.SelectedIndex;
        }
        protected void rdbList10_SelectedIndexChanged(object sender, EventArgs e)
        {
            //pega o index da lista de radio
            rbl10 = RadioButtonList10.SelectedIndex;
        }
        public void CarregarQuestionario(int a)
        {
            Label1.Visible = true;
            Label2.Visible = true;
            Label3.Visible = true;
            Label4.Visible = true;
            Label5.Visible = true;
            Label6.Visible = true;
            Label7.Visible = true;
            Label8.Visible = true;
            Label9.Visible = true;
            Label10.Visible = true;
            btnCorrigir.Visible = true;
            lbll.Visible = true;
            int x = 0;
            if (crud.Read(a) != null)
            {
                foreach (DataRow row in crud.Read(a).Rows)
                {

                    int id = (int)row["Id"];
                    string pergunta = row["pergunta"].ToString();
                    int certa = (int)row["certa"];
                    x++;
                    if (crud.Read2(id) != null)
                    {
                        DataSet ds = new DataSet(); ds.Tables.Add(crud.Read2(id));
                        questio.Add(new QuestionarioDados() { Ds = ds, Id = id, Pergunta = pergunta, certa = certa });
                    }
                    else
                        questio.Add(new QuestionarioDados() { Id = id, Pergunta = pergunta, certa = certa });
                }
                if (questio[0] != null)
                {
                    Label1.Text = questio[0].Pergunta;
                    RadioButtonList1.DataSource = questio[0].Ds;
                    RadioButtonList1.DataTextField = "Resposta";
                    RadioButtonList1.DataBind();
                }
                if (questio[1] != null)
                {
                    Label2.Text = questio[1].Pergunta;
                    RadioButtonList2.DataSource = questio[1].Ds;
                    RadioButtonList2.DataTextField = "Resposta";
                    RadioButtonList2.DataBind();
                }
                if (questio[2] != null)
                {
                    Label3.Text = questio[2].Pergunta;
                    RadioButtonList3.DataSource = questio[2].Ds;
                    RadioButtonList3.DataTextField = "Resposta";
                    RadioButtonList3.DataBind();
                }
                if (questio[3] != null)
                {
                    Label4.Text = questio[3].Pergunta;
                    RadioButtonList4.DataSource = questio[3].Ds;
                    RadioButtonList4.DataTextField = "Resposta";
                    RadioButtonList4.DataBind();
                }
                if (questio[4] != null)
                {
                    Label5.Text = questio[4].Pergunta;
                    RadioButtonList5.DataSource = questio[4].Ds;
                    RadioButtonList5.DataTextField = "Resposta";
                    RadioButtonList5.DataBind();
                }
                if (questio[5] != null)
                {
                    Label6.Text = questio[5].Pergunta;
                    RadioButtonList6.DataSource = questio[5].Ds;
                    RadioButtonList6.DataTextField = "Resposta";
                    RadioButtonList6.DataBind();
                }
                if (questio[6] != null)
                {
                    Label7.Text = questio[6].Pergunta;
                    RadioButtonList7.DataSource = questio[6].Ds;
                    RadioButtonList7.DataTextField = "Resposta";
                    RadioButtonList7.DataBind();
                }
                if (questio[7] != null)
                {
                    Label8.Text = questio[7].Pergunta;
                    RadioButtonList8.DataSource = questio[7].Ds;
                    RadioButtonList8.DataTextField = "Resposta";
                    RadioButtonList8.DataBind();
                }
                if (questio[8] != null)
                {
                    Label9.Text = questio[8].Pergunta;
                    RadioButtonList9.DataSource = questio[8].Ds;
                    RadioButtonList9.DataTextField = "Resposta";
                    RadioButtonList9.DataBind();
                }
                if (questio[9] != null)
                {
                    Label10.Text = questio[9].Pergunta;
                    RadioButtonList10.DataSource = questio[9].Ds;
                    RadioButtonList10.DataTextField = "Resposta";
                    RadioButtonList10.DataBind();
                }
            }
        }
    }
}