Microsoft"s instant messaging network is rejecting existing users of Windows Live Messenger when they try to sign in with a .Mac e-mail address. "Because of a recent system update, you must change the email address that you use to sign in to Windows Live Messenger. Until you change your email address, you won"t be able to use Windows Live Messenger," an error message explains. Microsoft explains the changes were required as a security measure because Office Live Communications Server 2005 SP1 enables messaging between the Windows Live Messenger Service and corporate IM systems. Some users have reported that the issue has been fixed, anyone still affected by the problem?