sql - System.ExecutionEngineException was unhandled -

i'm getting system.executionengineexception unhandled wcf service.

here code of iservice.cs

namespace myservice {    [servicecontract]   public interface iservice1   {      [operationcontract]      list<myemployee> findemployee(string uid);   } } 

and code of service1.svc.cs below

 namespace myservice  {     public class service1 : iservice1    {      public list<myemployee> findemployee(string uid)      {         dataclasses2datacontext context = new dataclasses2datacontext();         var res = r in context.myemployees r.empid == uid select r;         return res.tolist();      }     }  } 

this code works fine if change list string , select 1 column instead of entire row.

thanks in advance.