The solution is offline because its associated Team Foundation Server is offline

When opening a solution in Visual Studio 2008, I kept getting the following message in the Output window:

This solution is offline.  [Team Foundation Server:
http://server:8080/]
The solution is offline because its associated
Team Foundation Server is offline.

I kept having to go into the "change source control" and re-bind the solution. After a while, this began to get annoying. Then I found this post: http://www.eggheadcafe.com/software/aspnet/33487526/connecting-automatically.aspx. It turned out the solution was to set some registry keys. I navigated to HKEY_CURRENT_USER\Software\Microsoft\VisualStudio\9.0\TeamFoundation\Servers\ and changed "Offline" to 0 and "AutoReconnect" to 1. I've no idea how these got reset! (Please back-up your registry first if you want to try the same.)

System.ArgumentException: Illegal characters in path

This exception caused me a headache for an hour today on a development web site. After various rebuilds failed to cure the issue, I found out that the aspnet_wp.exe process had somehow become corrupted. Re-saves of the web.config file didn't help, so I opened Task Manager, killed the process and was back up and working again.