WCF error loading data

Question

Hello , I am found an error using WCF service. 
I am working on a silverlight project using the ADO.NET POCO generator.
The problem is that when I use a grid to print data from the Database, An exception occurs , and this is what is written : 
Server NOTFOUND and the location for the error is : 
System.Collections.ObjectModel.ObservableCollection<ESPRIT_FLEET_MANAGER3.ServiceReference1.Employees> _result = ((System.Collections.ObjectModel.ObservableCollection<ESPRIT_FLEET_MANAGER3.ServiceReference1.Employees>)(base.EndInvoke("loadall", _args, result)));

this is an example of a method that I used : 
 [OperationContract]
   public List<Employees> GetEmployees()
        {
            Esprit_FleetEntities db = new Esprit_FleetEntities();
            var emp = from e in db.Employees
                                   
                                    select e;
            return emp.ToList();
        }

In fact, When I don't use the POCO project and generator it works, but usiing this hierarchy causes a problem I think. 
So can you Help me PLEASE!
thanks