I'm getting the same thing: a sign-in that never ends. I tried the fixes mentioned in this thread and the others on the top page of this forum, and even uninstalled and reinstalled, and did a system restore to a date when it was known to be working, but no luck! I miss my WLM+Plus Live!
The WLM connection tester says "Your machine appears to have an invalid IP address" but I've gone over all my network settings, and even tried alternate settings with no success. Skype, Windows Messenger (the one that comes with Windows), Google Talk, Grouper, Groove, and Yahoo all work fine.
I am behind only a hardware firewall that I have been using for years and have never had problems with before. No Antivirus auto-protect is running, but I scanned with AVG after the problem started happening just in case it might find something. I have not changed any WLM or Plus settings in at least the last week, nor installed anything new except a Firefox plugin (Firebug).