Comments: ** Comment from web user: PiotrSobiegraj **
I've also had problems with compiling it under vs 2012 with strong name validation fails but I've found how to get around it:
1. download binary wersion for vs 2010 and install it (http://silverlight.codeplex.com/releases/view/78435)
2. While compiling project form solution Controls.Toolkit.sln you will get strong name validation fails.
3. Locate ddls failed to load in binary version (some are in Program Files (x86)\Microsoft SDKs\Silverlight\v5.0\Toolkit\dec11\Bin, some in Program Files (x86)\Microsoft SDKs\Silverlight\v5.0\Toolkit\dec11\Testing) and copy it to Binaries subdirectory in your downloaded source directory
4. This time project should compile without errors and in a moment controls should be added to vs2012.
I'm not sure if this 'mixed' version is production ready.