No debugging in Silverlight 4 with VS2010?

If you get this nice error message, you are probably lost, because there is no hints on WHY!!!???


Microsoft Visual Studio
Unable to start debugging. The Silverlight Developer Runtime is not installed. Please install a matching version.


Check your registry!!

When you create a Silverlight project, VS looks for the HKLM,SOFTWARE\Microsoft\Silverlight\Components\Debugging reg key to make sure you have the dev runtime. 
And when you debug, Silverlight looks for the HKLM\Software\Microsoft\.NETFramework\DbgpackShimPath reg key.

Thanks Amy!! Check out her blog about Silverlight and web dev


So your registry should have those keys and pointing to


On 64bit machines check





Both these keys should point to the same version (see my examples for Silverlight RTM)


योगेश चन्द्र उप्रेती said...

Thanks For Giving such a nice information.

Anonymous said...

This fixes it:

Re: Silverlight Developer runtime not installed
06-25-2010 4:04 PM |

Well after some more Googling I figured it out. There are 2 versions of the Silverlight browser runtime. One for end-users and one for developers.
The standard Silverlight 4 you install from MS does not work for debugging. Have to download it from here.
Thanks to this thread and post.
The "Silverlight managed debugging package" is part of the developer runtime, not the SDK or Tools. Make sure you have the latest version of the developer runtime installed (available at
If this post has solved your problem, please select 'Mark as answer'

- Jimmy Lewis
Microsoft SDET
Visual Web Developer Team

Anonymous said...

The information is very useful to identify and fix my problem. Other site just tell you to do things, but without root cause analysis. After all, with the help from this post, I deleted the silver light registry key and reinstalled the silverlight_tools for VS.NET 2010. Without deleting the key, no matter how I reinstall the silverlight_tools, it just doesn't work. By the way, I am in China, but the Great Firewall block this site, I have to us VPN to US and then access this site. How China gov doing this! It's shit.

Peter Gfader said...

My workmates in Beijing said they had no problems to access my blog. But that was 3 months ago... Maybe the Great firewall changed his mind again about


Anonymous said...

if visual studio launches the x64 bit version of IE, you will get the same nonsense..

Anonymous said...

No need to do these steps. Just uninstall all the versions including 4 and re=install it. It'll work.


o0Tao0o said...

Hi there,

Just wish to thank the first Anon poster. I tried to follow the registry fix, but the keys were missing completely. Easy to put in the version key, but not so easy to install the other one, sice this artice doesn't actually describe what the full key value should be!

Gave up on that, then visited the URL you provided (, Installed that and bingo! fixed!

Thanks again.

Anonymous said...

This page helped, thank you all:)

Anonymous said...

visited the URL you provided, Installed and fixed!!!


Mukesh Bhavnani said...

it worked 4 me..... great article.. thanks.. :-)

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