The AJAX version of the controls is causing this problem. You have upgraded Telerik.Web.UI.dll to use RadGrid AJAX, but this assembly contains also the rest of the RadControls. We use the RadUpload for uploading files. In the AJAX version, the RadUpload control was changed, which is causing the error you get now.
We suggest you to use the original RadControls that came with Sitefinity 3.2SP1. As the upgrade is not possible, this seems to be a solution. Another solution could be to use the AJAX version of the controls in different
application, and to include the page in which you have the RadGrid as an external page.
the Telerik team
Check out Telerik Trainer
, the state of the art learning tool for Telerik products.