Silverlight Multiple Table DataAccess Query

I have an SQL table [tbl_Test]
Contains the columns [Id], [Name], [Gender], [Age]
And another Table [tbl_Test_Addresses]
Contains the columns [AutoId], [UserId], [Address]

Now I am trying to access some data joining these two tables :

public List<Person> GetCustomerOrder()
DataClassesDataContext db = new DataClassesDataContext();

        var Test = (
                                from tbl_Tests1 in db.tbl_Tests
                                join tbl_Test_Addresses1 in db.tbl_Test_Addresses
                                on tbl_Tests1.Id equals tbl_Test_Addresses1.UserId
                                select new CustomerOrder {
                                    Id = tbl_Tests1.Id,
                                    Name = tbl_Tests1.Name

        return (List&lt;Person&gt;)Test ;

public class Person
public int Id { set; get; }
public string Name { set; get; }

It is not working.

But I have another table [Employee]
And when I try to fetch data in the following way

public List<Employee> GetUsers(string LastName)

DataClassesDataContext db = new DataClassesDataContext();

    var tests = from cust in db.Employees

                           /* where cust.LName.StartsWith(LastName)*/

                            select cust;

    return tests.ToList();


It can fetch data.

So I have problem as I try to join tables.

Can you tell me what I should do?