I exchanged notes with Josh Stevens at Microsoft about the issue, passing him a series of logs from VS2010, and he was able to diagnose the issue for my specific environment.
Telerik Inc developers, you'll want to take note!
It appears that the toolbox encountered an unexpected exception after the following log entry:
to get Toolbox items from Assembly
insufficient log information to say *why* that assembly caused an
exception, but we should be able to work around your problem by
That key refers to a pre-release Dev HotFix provided by Telerik. I've since updated to a new production release so I'm sure I don't need that anymore.
He directed me to this registry key:
I deleted that key. Josh suggested that I also delete either or both of these if they exist:
I deleted the second which was the only one there. (That one is mentioned elsewhere in this thread.)
Finally I deleted all of the TBD files (note, not TDB).
On restarting VS2010, not only was the problem with duplicate items fixed but so was the issue reported where VS does a long pause on this:
Loading toolbox content from package
If someone else does this and the problem does not go away, contact Josh, or you can contact me and I'll forward info to him.
Our take-away from this exercise is as follows:
- Before publishing assemblies, Telerik and others should be monitoring VS10 log files for otherwise silent exceptions thrown from their controls. I understand that I had a Dev HotFix but we've identified another source of exception notifications that Telerik should be using to QA all published assemblies.
- VS10 doesn't report this kind of toolbox control issue. I have been told that a forthcoming version of VS2012 does not duplicate toolbox items when an error like this occurs, and that developers will be told when something like this happens so that they can report issues to their control providers.
I hope this helps others using RadControls.