I have just encountered one issue while start the debugging one of my Silverlight 4 application. Silverlight 4.0 with VS 2010 was working fine few weeks back, but today when I started debugging to test one of my application, I got the error message as below.
I thought, It may be the problem with the Silverlight version which is selected for this project. I checked the Silvelight “Target Silverlight Version” from the Project Properties. But the Silvelight version was correct.
Then, I have also checked the associated hosting ASP.NET web application framework version. It was also targeting to .NET Framework 4.0 . So, there is no issue with my setup.
I started reinstalling the silverlight runtime and I received the below message :(
I was bit confused and looking for some solution over internet, and finally got the resolution from the thread Unable to debug silverlight . ohh. It was due some wrong version installation. I installed the Silverlight 4 developer runtime from the mentioned link .
After installation, the issue got resolved. :)
But not sure, why there was the mismatch of silverlight runtime version as it was working fine few weeks back. :( . Sorry, I am not spending any time to investigate it right now! :)
Hope, This may help you and save your some amount of time.