ASP.NET ช่วยหน่อยครับ มีปัญหาในการเชื่อมต่อฐานข้อมูลเวลาล็อคอินหน้าเว็บไม่ได้ครับ

<?xml version="1.0"?>
<!--
  For more information on how to configure your ASP.NET application, please visit
  http://go.microsoft.com/fwlink/?LinkId=169433
  -->
<configuration>
  <connectionStrings>
    <add name="dbConnectionString"
         connectionString="Data source=.\SQLEXPRESS;AttachDbFilename=|DataDirectory|\db.mdf;Integrated Security=True;User Instance=True"/>
  </connectionStrings>
  
	<system.web>
		<compilation debug="true"/></system.web></configuration>

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data;
using System.Web.Configuration;
using System.Data.SqlClient;


    public partial class Default : System.Web.UI.Page
    {
        protected void Login1_Authenticate(object sender,AuthenticateEventArgs e)
        {

            string UserName = Login1.UserName;
            string Pwd = Login1.Password;

            string strConn;
            strConn = WebConfigurationManager.ConnectionStrings["dbConnectionString"].ConnectionString;
            SqlConnection Conn = new SqlConnection(strConn);
            Conn.Open();

            string sqlUserName;
            sqlUserName = "SELECT UserName,Password FROM Members";
            sqlUserName += " WHERE (UserName = @UserName";
            sqlUserName += " AND Password = @Password)";

            SqlCommand com = new SqlCommand(sqlUserName, Conn);
            com.Parameters.Add("@UserName", SqlDbType.NVarChar).Value = UserName;
            com.Parameters.Add("@Password", SqlDbType.NVarChar).Value = Pwd;
            SqlDataReader dr = com.ExecuteReader();
            if (dr.HasRows)
            {
                Session["UserAuthentication"] = UserName;
                Session.Timeout = 1;
                Response.Redirect("MembersOnly.aspx");
            }
            else
            {
                Session["UserAuthentication"] = "";
            }
            dr.Close();
        }

    
    }