Please go to your control Panel ->Programs and Features
Make sure all the versions are same
If U are Using Microsoft Silverlight 4 Toolkit , Microsoft Silverlight 4 SDK 4.0.50826.0
then developer runtime which you installed should have a version
Microsoft Silverlight 4 Developer Runtime 4.0.50826.0
Go for the following link and download thw Developer runtime....
http://go.microsoft.com/fwlink/?LinkID=188039[
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