These are internal errors that are caught (in try/catch blocks) by the internal code of the RadWindow object. You see this errors because you have enabled "Break On All Errors" feature of FireBug. If you do not need to see these errors, I recommend you to disable them:
- Open FireBug
- Press Console tab
- Under the Console tab click the pause button on the left.
I hope this helps.
All the best,
the Telerik team
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