Have you tried to upgrade to the lastest Version of Messenger Plus!?
http://msgplus.net/download.php
If you have then reinstall Messenger Plus!. Or Shutdown all instances of Windows Messenger and MSN Messenger. Click start > run > type in "C:\Program Files\Messenger Plus! 3\MsgPlus.exe" (or whereever you installed Plus! to).
Once you have MsgPlus.exe in the task manager, open MSN Messenger.