Have you tried reinstalling?
Uninstall MSN first by going to contorl panel, add/remove programs, MSN Messenger 7.0, Remove.
Then download again from
messenger.msn.com
When you have done that, try running MSN messenger without plus and with plus to see if the problem still occurs.
EDIT: If you are running Messenger Discovery, try running MSN without Messenger Dicscovery.