The handwriting plug-in is causing this.
Firstly, the plug-in in the Plus! 3 Preferences dialog, in the Plugins section (msnhandwriting it's called, I believe).
If that doesn't work, look for the file MSNHandwriting.dll in the folder Plugins in the folder where you installed Plus!, most likely C:\Program Files\Messenger Plus! 3\Plugins and delete it after closing all Messenger related programs.
If you are on Windows 98 or ME, the plug-in will do this because it cannot work on those operating systems. If you're on Windows 2000/XP/2003, you have most likely installed it incorrectly. Look at
Ink/Handwriting Plugin Everything you need to know right here for more information
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