This error is caused by bug in the Silverlight Framework - we create CollectionView for the AppointmentsSource collection. Then when you switch to the first tab data context changed should be fired for the RadScheduleView and there we will remove handlers from this CollectionView. But the problem is that in SL we do not receive this event and cannot disconnect from the CollectionView. Then on second activation of RadTabItem which contains RadScheduleView it happened that a new instance of RadScheduleView is created and it tries to prepare the same CollectionView (group it) as the old RadScheduleView. This preparing raise CollectionView event that is also handled from the old ScheudleView which also tries to prepare the CollectionView and this cause an exception.
We have contacted Microsoft about this problem and we are waiting for solution.
Meanwhile you can set IsContentPreserved=True
to workaround the problem.
All the best,
the Telerik team
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