could not find Microsoft SDK silverlight v 4.0

could not find Microsoft SDK silverlight v 4.0

On starting Visual Studio 2010 express for windows phone its showing could not find Microsoft SDK silverlight v 4.0 error. It says System.NotSupportedException. At first the error was requested registry not found . Then I made changes in VPDExpress.vbproj.10.0 and VPDExpress.csproj.10.0 . Then it stopped showing that error but know this new kind of Silverlight v4.0 not found is generated . Please help me....

Thanks in Advance..

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