User control problem

[sonia sardana]

protected void btnLogin_Click(object sender, EventArgs e)
    {
        try
        {
            SqlConnection conn = new SqlConnection(ConfigurationManager.ConnectionStrings["ConnectionString"].ConnectionString);
            SqlCommand cmd = new SqlCommand("SELECT * FROM UserLogin", conn);
            conn.Open();
            SqlDataReader dr = cmd.ExecuteReader();
            while (dr.Read())
            {
                if (txtUserName.Text == dr[0].ToString())
                {
                    if (txtPassword.Text == dr[1].ToString())
                    {
                        Response.Redirect("FrmLogin.aspx");
                    }
                    else
                    {
                        lblError.Text = "UserName & Password do not match";
                    }
                }
                else
                {
                    lblError.Text = "UserName & Password do not match";
                }
            }
        }

        catch (Exception ex)
        {
            Response.Write(ex.Message.ToString());
        }
    }

I call user control in Frmlogin.aspx page. First time i run the form,it runs.Now when i runs the Frmlogin.aspx page error is there
Disassembly cannot be displayed. The expression has not yet been translated to native machine code.

Wats dis error means?Can u tell me?