Silverlight 4.0 Debugging Issue – “Unable to start Debugging.The Silverlight Developer Runtime Not Installed. Please Install a matching version” – Resolution

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.

Thanks !

.NET 4.0, Silverlight 4 ,

Written by Abhijit Jana

Technology Leader, Technical Strategist, Solution Architect, Development Consultant, and a Trusted Technology Advisor with more than 13 years of experience in the IT industry with expertise in Development, Architecting, Engineering, Consulting, and Services Delivery. I am a former Microsoft MVP, Author of "Kinect for Windows SDK Programming Guide" and "HoloLens BluePrints" books, and founder of The Daily .NET Tips. To know more about me visit the "About Me" page.


  1. Thank you so much for the blog. I also had the same problem. Everything was fine for months up until last week. Not sure what’s going on!


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