I found this on a competing forum, it solved the issue on two Vista Business stations in our office......
"The problem comes from the latest updates of MSN which create some conflicts of registry. I have resolved my problem by doing following:
1- click RUN from START menu and type REGEDIT:
2- follow path: HKEY_CURRENT_USER/SOFTWARE/MICROSOFT/MSNMessenger/PerPassportSettings.
3- under PerPassportSettings, you should find 2 folders named with a series of numbers. Delete both folders including their sub-files... and restart MSN."
As with the user who suggested this fix I found one machine with several folders and I deleted all with the exception of the folder named "0". Good luck.