I’ve almost completed a project in Silverlight 3 and decided to export it to Silverlight 4 but after the export was made, with Blend 4 Beta … I couldn’t debug both my solutions (Silverlight and Web Application).
After searching the web for some solutions and trying some of them I’ve found the simplest and the correct one …
Just Enable the Silverlight debugging from Web Project ->Properties->Web tab->Debuggers
Solution was taken from here.
Have fun with Silverlight!