I found out what the cause, i have an "ID" Field that i use to delete from the database, and it work fine if i donot update, that ID field its hidden, from people, when i insert or update, when i try to delete i receive a field with  .
Hope this helps. Please excuse us for any inconvenience this might have caused you.
Regards,
Eyup
Telerik
If you want to get updates on new releases, tips and tricks and sneak peeks at our product labs directly from the developers working on the RadControls for ASP.NET AJAX, subscribe to the blog feed now.