Thanks for reporting this. The exception is caused by a bug in Silverlight
we already managed to workaround in the 2011 Q1 Beta version (which should be visible in your account).
The controls that lead to the error are namely TableSizePicker and HighlightColorPicker, so in your current version (Q3 2010) you shouldn't add more that one instance of them in your XAML.
Don't hesitate to contact us if you have other questions.
the Telerik team
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