https://login.live.com/ppsecure/md5auth.srf?f=9

Do you have a question?

This is what I get, when I go to the link you supplied. A simple message that my user name/password is incorrect. Is that what you get?

Microsoft Messenger is apparently send a username/password combination that Windows Live doen't like.

What if you just enter your username/password into a plain old Live login?

At this point this looks like a Microsoft support issue for Messenger.

At that point you have a problem with Microsoft--Safari is just the vehicle delivering the message that Microsoft's servers don't know who you are. Because that error message is coming from Microsoft's web server and not your Mac. The more interesting issue is not that you can't log in, but that Messenger somehow still seems able to do so.

Frankly, this is the wrong forum for your issue, since it deals with the interaction of Microsoft Messenger and Microsoft Live (which, as I recall, Microsoft is transitioning one more time to whatever the new name will be). The real problem is that you cannot log into live.com.

Obviously the first question is going to be whether you are *SURE* you are using your Windows Live username and password. Because right now it looks like your problem is that you are using the wrong username and password, which is exactly what Microsoft is telling you.