error in Linq to SQL

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LINQ

im refering: Microsoft.press.microsoft.ado.net.4.step.by.step.oct.2010
I was trying linq to sql, but i get this error:"The type 'ADODOTNET.Emp' is not mapped as a Table."

public class SalesOrder : DataContext
{
        // ----- Constructor establishes database connection.
        public SalesOrder(string connectionString) : base(connectionString) { }
        // ----- Table definitions to link with database.
        public Table<Emp> Employee;

}

Emp table has 4 coloumns:
ID
fname
Lname
Salary

I was firing below linq query:

using (SalesOrder context = new SalesOrder(linkToDB.ToString()))
            {
                var linqresult = from cu in context.Employee
                                 select new { CustomerID = cu.ID, CustomerName = cu.LNAME };
            }