Unable to start debugging. The Silverlight Developer Runtime is not installed

Trying is run the Silverlight 4 solutions. I’m going through the tutorial and come across this error: Unable to start debugging. The Silverlight Developer Runtime is not installed. Please install a matching version.

It can be found here:

http://go.microsoft.com/fwlink/?LinkID=188039.

Windows Phone 7

Very good Architectural write-up on Windows Phone 7 at CodePlex:

Windows Phone 7 Developer Guide P&P

Project’s scope