ok... I am using windows XP, latest non-beta messenger, latest non-beta messenger plus installed and some plugins, I do not know which ones right now.
If you type in a message starting with /, usually the command reference window appears. It is small and for the many entries, you can scroll. Do so and inform your partner to send a message to you right at this moment (when you are using the slider on the right hand side to scroll).
Windows Live Messenger will crash with a possibility to send an error report.
Edit: The exact error message on english language based client systems is similar to the one stated in
this thread (I'm using german windows XP without MUI...)