if you have windows messenger and msn messenger both trying to run at the same time, one signs the other out, even if you think you logged off it still is running in the background(windows messenger) and just want the new msn6 . go to add remove programs, remove msn6 messenger, then click add remove windows components take the check out of windows messenger, click next then finish, now download the new msn messenger, if you dont all ready have the installer,
http://messenger.msn.com/
before you install, go to C: program files\messenger and delete or rename the entire folder, reboot, now after rebooting if you get a error just click it off, and install msn6, reboot again. works fine, any other method i have tried has not worked, as soon as you open outlook,ol express, or any other app. that uses windows messenger brings it right back if not done this way.maybe other ways, but i am not aware of them, even disabling its services key does not stop the windows messenger totally.