RadControls for ASP.NET AJAX are compatible with both 64bit and 32 bit OSs and we are not aware of any 64 bit problems.
Please, note that we offer special RadControls for SharePoint 2010 wrappers designed especially for SharePoint 2010. You can find more information about them in the following page http://sharepoint.telerik.com/Pages/default.aspx
and in the documentation: Installing RadEditor & RadGrid Web Parts on SharePoint 2010
the Telerik team
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