在DataService.cs中，有方法：

 public IQueryable<TabUser> GetTabUser()
        {
            return this.ObjectContext.TabUser;
        }

  [Invoke]
        public int GetTabUserCount(string userName)
        {
            var result = from a in ObjectContext.TabUser
                         where a.Name.Contains(userName)
                         select a.ID;
            return  int.Parse(result.Count().ToString());
        }

在silverlight页面的调用代码：

  　　public void SelectTabUser()
        {
            dc.Load(dc.GetTabUser(), OnSelectTabUser, null);
        }        

        public void GetUserPageCount(string UserName)
        {
            dc.GetUserPageCount(UserName，OnGetUserPageCount, null);
           
        }

        private void OnSelectTabUser(LoadOperation<TabUser> lop)
        {
            if (lop.HasError)
            {
                MessageBox.Show(string.Format("错误提示: {0}", lop.Error.Message));
                lop.MarkErrorAsHandled();
            }
            else
            {
                TabUser = lop.Entities;               
            }
        }

        private void OnGetUserPageCount(InvokeOperation<int> invOp)
        {
            if (invOp.HasError)
            {
                MessageBox.Show(string.Format("错误提示: {0}", invOp.Error.Message));
                invOp.MarkErrorAsHandled();
            }
            else
            {
                int pageCount = invOp.Value;
            }
        }

调用SelectTabUser方法的时候放回的数据是正确的，但是调用GetUserPageCount方法的时候，invOp.Error.Message提示Invoke operation 'GetUserPageCount' fail。请高手指点究竟哪里代码出现问题了，帮忙解决此问题！！