This could be a bug with the nadwriting plugin for plus!
Close all instances of MSN Messenger and Windows Messenger you're running completely.
Delete the file MsnHandWriting.dll from your Messenger Plus! Plugins directory. (default directory is: c:\program files\messenger plus!3\plugins)
Go to add/remove programs in the software tab in your configuration settings. Look for "Ink Redistributables" or "InfoPen", click it and uninstall it.
Restart your computer, to make sure everything is completly removed
Also see
andrey's reply to Contacts! disappear