Are you getting the error below when working with Silverlight projects?

Could not load file or assembly 'System.Windows, Version=2.0.5.0, 
Culture=neutral, PublicKeyToken=7cec85d7bea7798e' or
one of its dependencies.

It's a bit of an odd one. The solution that works for me is to re-register System.Core and System.Windows in the GAC. Use the commands below.

32 Bit System

"C:\Program Files\Microsoft SDKs\Windows\v7.0A\bin\NETFX 4.0 Tools\gacutil" /i "C:\Program Files\Microsoft Silverlight\4.1.10111.0\System.Core.dll"
"C:\Program Files\Microsoft SDKs\Windows\v7.0A\bin\NETFX 4.0 Tools\gacutil" /i "C:\Program Files\Microsoft Silverlight\4.1.10111.0\System.Windows.dll"  

64 Bit System

"C:\Program Files (x86)\Microsoft SDKs\Windows\v7.0A\bin\NETFX 4.0 Tools\gacutil" /i "C:\Program Files\Microsoft Silverlight\4.1.10111.0\System.Core.dll"
"C:\Program Files (x86)\Microsoft SDKs\Windows\v7.0A\bin\NETFX 4.0 Tools\gacutil" /i "C:\Program Files\Microsoft Silverlight\4.1.10111.0\System.Windows.dll"  

So far I am yet to understand why this happens - if anyone can shed any light please comment!