Can you please verify that you followed the upgrade instructions from this KB article
on our site? Generally, the hotfix build you applied should work in the same way as the latest official version 2008.1.515 of RadGrid for ASP.NET AJAX.
If the issue persists, please isolate a small working version of your project and send it enclosed to a formal support ticket. I will test it locally and will get back to you with my findings.
the Telerik team