An exception of type 'system.invalidoperationexception' occurred in system.data.dll

An exception of type 'System.InvalidOperationException' occurred in System.Data.dll

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Mvc;
using System.Data;
using System.Data.SqlClient;
using WebApplication3.Models;

namespace WebApplication3.Controllers
{
    public class ProductController : Controller
    {
        String cs = @"Data Source = DESIGNER\\SQLEXPRESS; Initial Catalog = MvcCrudDB; Integrated Security = True";

        [HttpGet]
        public ActionResult Index()
        {
            DataTable dtblProduct = new DataTable();
            using (SqlConnection con = new SqlConnection(cs))
            {
                con.Open();
                SqlDataAdapter da = new SqlDataAdapter("SELECT*FROM Product",con);
                da.Fill(dtblProduct);
                con.Close();
            }
            return View(dtblProduct);
        }