I Can't add or remove using ria services in my SL4 project

Question

Hi ..
I built this SL4 project .. and it was working perfectly, after while I re-opened the project and pressed F5 to try it again.
After I add new item in Data Form, filling the required field and doing "SubmitChanged()" I get "Code : 4004 error message" .

I'm using Entity Framework + RIA services, I used EF profiler to see if the Linq to entity phrase transformed into SQL, but it didn't so I thought it maybe and error happening when the RIA trying to send the request to server ...

Any thing can I do to solve this problem ? PS : I tried to work on new project in new solution, but I got the same problem .

Thanx in advanced .