Not everything in WPF will translate directly to Silverlight (like the synchronous Socket class methods, ugh.) What does the namespace "x" translate to? There should be an "xmlns:x=http://<...>" at the top of the XAML file. Chances are, the "x" namespace is pointing to an assembly that doesn't contain a definition for Type. If the XAML code was copied and pasted, it most likely points to the WPF assembly that contains Type, but Silverlight will probably be different.