Vista is incompatible with Windows Live Messenger.

The Windows Vista beta version conflicts with Windows Live Messenger 8.0 (official version) and 8.1 (beta version). It was originally thought that this issue would be resolved in the official release of Vista. However, according to feedback from multiple users of the official Vista version, the problem still hasn't been resolved. One tester said, "After running for three hours on Vista, Windows Live Messenger began to experience continuous conflicts. Sometimes it would conflict four times in a row."