MSN Messenger not working under Vista?

For some reason, I can'tseem to get Windows Messenger 8, or MSN 7.5, to work on my PC. I can do seemingly everything else - browse the web, POP/SMTP mail, FTP, Bittorrent, but I just can't get MSN to work!

Any suggestions/ideas?

This has happened in sdliub 5308, 5342, 5365 and 5381.