If you’ve recently canceled your .Mac/MobileMe subscription, you may be having a problem where your Mac doggedly tries to connect to MobileMe and presents a log-in window at random. When this happens, entering the old MobileMe credentials won’t work, and clicking cancel seems to be the only way to get rid of the window.
Over on the Apple Discussion board, poster “Maria Folsom” writes:
“I suddenly get a message box on my screen that requests my .mac usernameand password for .mac. I haven’t been a .mac (or MobileMe) member for months. When I enter my old password and user name, another message says it is invalid. Very annoying, as this keeps popping up now suddenly for no reason.”
According to MacFixIt, this problem is because the old account username and password have been left in the MobileMe or .Mac control panel, which is trying to authenticate and connect to the service periodically. When this happens and the credentials do not work because the account was canceled, MobileMe will prompt for correct credentials.
The current fix is as follows:
Go to the MobileMe or .Mac system preferences and delete the log-in and password information stored there. Additionally, you may also try removing any MobileMe or .Mac entries from your keychain with the Keychain Access utility. Doing this should prevent an improper log-in attempt by MobileMe, which results in this authentication window.
Try it again from here and let us know how it goes in the comments.