Good evening Thomas,
You didn't happen to install the handwriting plug-in earlier, have you? This plug-in is known to cause problems like that when installed on Windows 98/ME or other versions that (sometimes) don't support it.
If you have, close down all Messenger related applications and remove the file MsnHandWriting.dll from your Messenger Plus!\Plugins directory, most likely the default C:\Program Files\Messenger Plus! 2\Plugins.
More information can be found at
http://shoutbox.menthix.net/showthread.php?tid=22276.
Good luck
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