System.IO.File Load Exception

HI,

I am getting following xaml error. How to overcome this let me know.

System.IO.FileLoadException
Could not load file or assembly 'System.Windows.Controls.Layout.Toolkit, Version=3.5.40128.1, Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of its dependencies. Operation is not supported. (Exception from HRESULT: 0x80131515)