IsSelectionMiniToolBarEnabled is a property we introduced in Q3 2010 Beta. If it is not visible, you have probably referenced an older version of the control. That would also explain your issues with the selection, too.
Please, make sure that you have the following references in your Silverlight application and that they point out to the folder which contains the Q3 Beta DLLs:
All the best,
the Telerik team
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