Error LINQ : Query A SQL Server Database !

I have an example : A Simple Database Query using LINQ to SQL

Before creating the project, I using SQLmetal to generate the Nosthwind Entity Classes "Northwind.cs" 

c:sqlmetal /namespace:nwind /code:Northwind.cs /pluralize /functions /sprocs /views "C:CongChinhNorthwindNorthwind.mdf"

and then, I add the Northwind.cs in my project.

CODE  1 using System;
2
3 using System.Linq;
4
5 using System.Text;
6
7 using nwind;
8
9
10
11 namespace Ex
12
13 {
14
15 class Program
16
17 {
18
19 static void Main(string[] args)
20
21 {
22
23 Northwind db = new Northwind(@"Data Source=.SQLEXPRESS;Initial Catalog=Northwind");
24
25 var cust =
26
27 from c in db.Customers
28
29 where c.City == "Rio de Janeiro"
30
31 select c;
32
33 foreach (var kh in cust) //---> SQLException was unhandled
34
35 Console.WriteLine("{0}", kh.CompanyName);
36
37 Console.ReadLine();
38
39 }
40
41 }
42
43 }
 But when I run the program. It throws a SQLExecption : Login failed for user ''. The user is not associated with a trusted SQL Server connection.I'm using SQLExpress and server name : CONGCHINHSQLEXPRESS and Windows Authentication

I don't know how to solve this problem. Somebody help me,please !