Performing Submit Form using C #

The following HTML login form is available

  <form action="/Home/Login?ReturnUrl=%2f" method="post">
     <input name="__RequestVerificationToken" type="hidden" value="W3ndyLx5kkFIy_QKjOGhEYQoHFtF4kIMFxLIG42t2r5tJJKwnzCy1iMmLw8SFH6yIm7DnHiQqKAmOhKS-PSDnDDzNcfjxNWCCEDthaA5mAE1" />    
     <div  style="width: 40%; margin-left:36%;" >

    <h2>Login</h2>

    <div class="form-group">
        <label for="Usuario">Usu&#225;rio</label>
        <input class="form-control" data-val="true" data-val-required="Usuário Necessário" id="Usuario" name="Usuario" placeholder="Digite seu usuário" type="text" value="" />
        <span class="field-validation-valid" data-valmsg-for="Usuario" data-valmsg-replace="true"></span>
    </div>
      <div class="form-group">
        <label for="Senha">Senha</label>
        <input class="form-control" data-val="true" data-val-required="Senha Necessária" id="Senha" name="Senha" placeholder="Digite sua senha" type="password" />
         <span class="field-validation-valid" data-valmsg-for="Senha" data-valmsg-replace="true"></span>
      </div>

      <button type="submit" style="width: 100px" class="btn btn-success" value="Entrar">Entrar</button>
  </div>
</form>

I'm trying to login to this page using C #:

    private string Realizar(string url, string Usuario, string Senha)
    {
        string resultado = string.Empty;
        string strPost = "Usuario=" + Usuario + "&Senha=" + Senha + "&ReturnUrl=//";
        Stream myWriter = null;

        HttpWebRequest request = (HttpWebRequest)WebRequest.Create(url);
        byte[] send = Encoding.Default.GetBytes(strPost);
        request.Method = "POST";
        request.ContentLength = send.Length;
        request.ContentType = "application/x-www-form-urlencoded";
        request.Credentials = CredentialCache.DefaultCredentials;

        try
        {
            myWriter = request.GetRequestStream();
            myWriter.Write(send, 0, send.Length);
        }
        catch (Exception ex)
        {
            return ex.Message;
        }
        finally
        {
            myWriter.Close();
        }

        var response = (HttpWebResponse)request.GetResponse();
        if(response == null)
        {
            return "Erro";
        }
        using(StreamReader reader = new StreamReader(response.GetResponseStream()))
        {
            resultado = reader.ReadToEnd();

            reader.Close();
        }

        return resultado;

    }

However, when you run the function, it returns the following exception: The remote server returned an error:

  

(500) Internal Server Error.

Can anyone help me?