I have looked around a bit, and I did not find any threads that described this problem, so here goes:

I'm using:
-Windows Live Messenger 8.0.0792.00
-Messenger Plus! Live 4.01.0.240
on Windows XP Home Edition SP2

The bug that I have run into is as follows. If a second copy of WLM is run (polygamy) while the first copy has the Messenger Lock feature activated, the WLM copy that is locked crashes. (Windows Live Messenger has encountered a problem and needs to close.. blah blah blah.. Send error report? (yes/no).) This probably isn't something that happens a lot, but I do think that it ought to be fixed because the situation can still occur.

P.S. Love MsgPlus and MsgPlusLive, Thanks Patchou!

It hasn't crashed on my work machine, but I can't get it out of Lock.

Cant reproduse it here. I can lock/unlock both messengers...

I think i had that problem a little while ago, only mine tries to sign two messengers in at the same time.

I can't reproduce... can you try to find a specific cause for the problem? thanks.

I don't know if this is relevant, but I have auto-sign in enabled for Messenger, so when I run the second copy, it signs in automatically, and that's when the locked Messenger crashes.
After a bit more experimenting, I found that this problem ONLY occurs if the first Messenger had the contact list open at the time that it was locked. Other windows such as conversations do not seem to affect the problem, just the main contact list. That makes me think (just a guess) that the problem is caused by the locked Messenger trying to do something with the contact list window, and crashing because Messenger Lock is preventing it from doing so. It doesnt seem like any of the options for Messenger Lock affect whether it crashes or not.

Hope this helps.

thanks for the extra info.

please send me an email to mplus@patchou.com and we'll work on that together.

I've got the same problem, when i press the shortcut, the lock doesn't work, if i launch 5 WML, the 4 first can't be locked.