You can obtain a full stack-trace if you temporarily disable the AJAX updates on the page.
If you're using RadAjaxManager set EnableAJAX to "false".
In case you're using update panels set EnablePartialRendering on the ScriptManager to "false":
We should be able to help with the full stack trace at hand.
You should also be aware that there's a known issue
with the RadAsyncUpload in the official Q2 release. Our recommendation is to update to internal build 2010.2.722 before continuing.
I hope this helps.
the Telerik team
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