Numerous users in Apple's support forum had been complaining that Live Messenger displays an error code which prompts the user to change the e-mail address to log-in to the service.
A user's e-mail address in Windows Live is also the user's ID, meaning that anyone switching e-mail addresses would need to migrate all contact information to the new account.
The error message attributed the issue to a "system update", and seems to have affected only users with Mac.com email addresses which are part of Apple's .mac internet suite.
Users began reporting the issue on Apple's support site last week, noting that the service appeared to be accepting mac.com addresses again on Thursday.
A Microsoft spokesperson told vnunet.com that the service had encountered an error which asked .Mac users to change their addresses.
The issue was down to an internal error that occurred during "routine testing " and has since been corrected. Apple had no comment.
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