Interesting little bug that I ran into today. If you reference a Windows Forms project from another Windows Forms project using the Project Reference dialog, you will get this weird error:
Could not find file 'Microsoft.Windows.CommonLanguageRuntime, Version=2.0.50727.0'
There is actually a KB on it, but it doesn't show up in Google, or of course in MSDN search:
http://support.microsoft.com/?kbid=907757
Learn something new every day. Service Pack 1, anyone?