Asp.net MVC: the underlying provider failed to open. error

Question

Help me where I am wrong

 

Here with I attach my mvc code.

 

#view

@model MVCDemo2.Models.Employee
@{
ViewBag.Title = "Employee Details";
}
<h2>Employee Details</h2>
<table style="font-family:Arial">
<tr>
<td>
<b>Employee Id:</b>
</td>
<td>
@Model.EmployeeId
</td>
</tr>
<tr>
<td>
<b>Name:</b>
</td>
<td>
@Model.Name
</td>
</tr>
<tr>
<td>
<b>Gender:</b>
</td>
<td>
@Model.Gender
</td>
</tr>
<tr>
<td>
<b>City:</b>
</td>
<td>
@Model.City
</td>
</tr>
</table>

#controller

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Mvc;
using MVCDemo2.Models;
namespace MVCDemo2.Controllers
{
public class EmployeeController : Controller
{
public ActionResult Details(int id)
{
EmployeeContext employeeContext = new EmployeeContext();
Employee employee = employeeContext.Employees.Single(emp => emp.EmployeeId == id);
return View(employee);
}
}
}

#EmployeeContext

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Data.Entity;

namespace MVCDemo2.Models
{
public class EmployeeContext : DbContext
{
public DbSet<Employee> Employees { get; set; }
}
}

#webConfig

<connectionStrings>
<add name="EmployeeContext" connectionString="Data Source=ADMIN-PC3\SQLEXPRESS;Initial Catalog=employee;Integrated Security=true"
providerName="System.Data.SqlClient"/>
</connectionStrings>

but Run time Error "EntityException was unhandled by user code" The Underlying provider failed on on Open.