Sorry for the late reply. If you haven't fixed it already, then here's what you do:
Log in on the account that keeps crashing WLM on a DIFFERENT computer (one with more RAM than the one you use). Then, when any offline message(s) come up, wait at least 30 seconds before closing it. Log off and log back on the same computer to make sure the offline message(s) doesn't/don't pop up again. Log off, then go back to the computer you were using before and log in there. You shouldn't have a crash this time. Now to prevent it from happening again, while still logged in, go Tools>Options>Messages and under "Offline Instant Message Settings", check the radio button next to "Show a link to my offline messages in the main window". You may also want to make sure "Show Windows Live Today after signing in to Messenger" is unchecked (it's in the same window under "General"). Click OK and you're done.
Also, another cause may be someone messaging you as soon as you sign in, in which case you sign in as "Appear Offline" and wait for everything to load before switching your status to "Online".
Hope this helps.
EggHeadCafe.com - .NET Developer Portal of Choice
http://www.eggheadcafe.com