Returnurl=%2f проблема в ASP.NET проверка подлинности форм

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When I Loged into the web and clicked on Login, it was navigating to the LogIn page but it adds 'ReturnUrl=%2f' to the URL. For example, authentication.aspx?ReturnUrl=%2fAXERP-UAT%2fsubsystem%2fmain_menu.aspx.After Login, it should point to this page subsystem/main_menu.aspx. Can anyone help me? Thanks a lot.

Что я уже пробовал:

----------------------------------web.config

<appSettings>
    <add key="ConnectionString" value="AX-UAT;Integrated Security=false;Initial Catalog=SBG_AX_2020;User ID=sbax;Password=sbax;Connection TimeOut=99999" />
  </appSettings>

<authentication mode="Forms">
      <forms name="AXERP-UAT" loginUrl="authentication.aspx" protection="All" path="/" timeout="1500" />
    </authentication>
    <authorization>
      <deny users="*" />
    </authorization>

----------------------------КОДИРОВАНИЕ С#

protected void authenticate(object sender, EventArgs e)
    {
        if (txtUsername.Text == null | txtUsername.Text == string.Empty)
        {
            ClientScript.RegisterStartupScript(this.GetType(), "alert", "alert('Error? Please enter email address');", true);
            return;
        }

        if (txtPassword.Text == null | txtPassword.Text == string.Empty)
        {
            ClientScript.RegisterStartupScript(this.GetType(), "alert", "alert('Error? Please enter password');", true);
            return;
        }

        SqlConnection con_Check_UserData = new SqlConnection(ConfigurationSettings.AppSettings["ConnectionString"]);
        SqlCommand cmd_Check_UserData = new SqlCommand();
        try
        {
            cmd_Check_UserData.CommandText = "select * from VIEW_LOGIN where username = '" + txtUsername.Text + "' and password = '" + txtPassword.Text + "'";
            cmd_Check_UserData.Connection = con_Check_UserData;
            con_Check_UserData.Open();
            System.Data.SqlClient.SqlDataReader rd_Check_UserData = cmd_Check_UserData.ExecuteReader(System.Data.CommandBehavior.CloseConnection);
            if (rd_Check_UserData.HasRows)
            {
                while (rd_Check_UserData.Read())
                {
                    rd_Check_UserData.Read();
                    ClientScript.RegisterStartupScript(this.GetType(), "alert", "alert('Login Successful');", true);
                    Response.Redirect("subsystem/main_menu.aspx");

                    FormsAuthentication.RedirectFromLoginPage(txtUsername.Text.ToLower(), false);
                }
            }
            else
            {
                ClientScript.RegisterStartupScript(this.GetType(), "alert", "alert('Invalid Username/ Password');", true);
                return;
            }
        }
        catch (Exception ex)
        {
            con_Check_UserData.Close();
            Lbl_Message.Text = ex.Message;
            //Response.Redirect("main_menu.aspx");
            return;
        }
        finally
        {
            con_Check_UserData.Close();
        }

        con_Check_UserData.Dispose();
        cmd_Check_UserData.Dispose();
        con_Check_UserData = null;
        cmd_Check_UserData = null;

    }

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