Might be a plugin or Smileycentral.
If you use Smileycentral,
uninstall that and all will be fine again.
Another thing that causes this is previous use of the handwriting plugin, with MSNM 7 you don't need it anymore. Solution to that is: exit MSNM, go to the plugins folder (C:\Program Files\MessengerPlus! 3\Plugins most likely, could be in another left over plugins folder of Plus! aswell, so check those too) and delete handwriting.dll.
/ 
