Input string was not in an incorrect format

I'm getting the "Incoming Sequence was not in an incorrect format" when I make an inclusion in the database and update the gridview.

But this only happens for the first record. From what I've tried I've noticed that the error comes from the C # code and not from the database.

The code in question:

<asp:GridView ID="gvEfluentes" runat="server" AutoGenerateColumns="False" DataSourceID="odsCaixasSeparadoras" OnDataBound="gvEfluentes_OnDataBound" SkinID="noSort">
    <Columns>
        <asp:BoundField DataField="Nro_caixa" HeaderText="Caixa Nº" SortExpression="Nro_caixa">
            <HeaderStyle Width="100px" />
        </asp:BoundField>
        <asp:BoundField DataField="Desc_modelo" HeaderText="Modelo" SortExpression="Desc_modelo">
            <HeaderStyle Width="100px" />
        </asp:BoundField>
        <asp:BoundField DataField="Outro_modelo" HeaderText="Outro modelo" SortExpression="Outro_modelo">
            <HeaderStyle Width="100px" />
        </asp:BoundField>
        <asp:BoundField DataField="Desc_eficiencia" HeaderText="Eficiência" SortExpression="Desc_eficiencia">
            <HeaderStyle Width="100px" />
        </asp:BoundField>
        <asp:BoundField DataField="Desc_recebe" HeaderText="Receber de" SortExpression="Desc_recebe">
            <HeaderStyle Width="100px" />
        </asp:BoundField>
    </Columns>
</asp:GridView>
<asp:ObjectDataSource ID="odsCaixasSeparadoras" runat="server" DataObjectTypeName="FEPAM.CADASTROS.DAL.PostosCaixasParametros"
    OldValuesParameterFormatString="original_{0}" SelectMethod="GetDadosPostoCaixaParametro"
    SortParameterName="SortExpression" TypeName="FEPAM.CADASTROS.BLL.PostoCaixaParametro">
    <SelectParameters>
        <asp:SessionParameter Name="ptcb_id" SessionField="PTCB_ID" Type="Int64" />
        <asp:Parameter Name="SortExpression" Type="String" />
    </SelectParameters>
</asp:ObjectDataSource>