Paul,
This can also happen when using source code control with readonly checked out files.
> I just walked through all the classlibs manually (which was a pain considering how many I've got). I decide to restore from last night (a ZIP file) and found out what was causing the problems. Somehow one of the classlibs got marked as read-only (WinZip complained about it when it tried to overwrite it). So it's working now. Thanks for the suggestions.