sorry ben - gotta read more closely...
jcrim-
What has happened is either that someone else is currently trying to sign in, and you're in line behind them, or AC crashed while someone was signng in. AC creates a file with the extension .lck during the sign in process. Delete this file, and you'll be good to go. If you read the file with a text editor, it will tell you not to delete the file unless you're sure noone else is signing in. Heed its advice.
Hope that helps.
Wes