Messenger

One of my users is locked out of his messages in Messenger.

I am not sure which is best to use, Windows Messnger or MSN, the email address is ABC@msn.com.
Using Win XP SP1, the messages worked till last week in Hotmail, but are no longer available, and the user can not say whether he has changed something or if Microsoft has upgraded something. When I tried to log in I got a message that Windows does not support .Net Passport you are signed in to. Visit the Hotmail site, when I did, I was not able to download the required file.
Help!