The VS11 Beta Release of RadControls for Silverlight and RadControls for WPF includes limited support for VS11 Beta. This is because we encountered an issue loading the toolbox items automatically. It's the same issue as the one you've described in your posts.
Here is an blog post with further details: http://blogs.telerik.com/blogs/posts/12-03-13/telerik-xaml-controls-and-the-vs11-beta-release.aspx
. It also describes how to add the controls to the toolbox manually.
As a workaround, we found that if the toolbox is closed before opening a WPF/Silverlight form, the toolbox items are loaded. Still, this is not reliable solution, but can help is some cases.
We have reported the issue to Microsoft and we expect it to be fixed for the next official release.
the Telerik team
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