If you run Microsoft Messenger (MSN) on a Mac OSX and you keep getting the message “failed to login” then you have to remove these files in ~/Library/Preferences/Microsoft folder :
com.microsoft.Messenger.plist com.microsoft.MessengerDaemon.plist Microsoft Messenger User Cache Microsoft Messenger User Cache.plist
(short posting mostly to serve as a reminder for a myself because I keep on forgetting the exact path)