Unfortunately, I didn't have much luck on this end either.
I talked with a DSL provider here and their tech said it sounded like you needed to open some ports, but he had no advice for me on how to do that for your provider. Yahoo was no help at all (Imagine that!) with the exception that they list the ports Messenger uses. (5050 - 5070)
Was your old version of Messenger working ok? You might want to move back to the older version just to get back up and going. This problem has me pretty perplexed and I'm determined to find the solution, but it could be a while before I do get to the bottom of it. Sure wish I knew more about DSL...I connect through wireless LAN.
Sorry I couldn't be more help, but I'll be ever vigilant for the solution and post back here if I find it.
Anybody else got any thoughts on this problem? Feel free to jump in!!!