I'm having almost the same problem.
But my MSNM crashes on startup, when loggin in, it just stops...
I tried MSNM 7.5 & MSNM 7.0
and somehow Windows Messenger won't start either.
I also uninstalled Plus!
Nothing seems to work
I installed 512 MB of RAM, that's when it started...
EDIT: Just removed the RAM again and it works again.
What should I do???
EDIT2: Restarted MSN and got the same thing, tried a system restore, MSN worked again, but registry was f*cked up, so I had to repair MSN to be abled to install Plus!, and guess what... the same thing...
Well, I guess I can put the extra ram back, as MSN doesn't work with or without it...
EDIT3: Put the RAM back in, when I start MSNM with my second account it lags for like ~5 min and then starts normally, with my first account it takes like ~15 min to start.
I deleted my Documents and Application Data/MSN Messenger folder too, but that didn't help. Also cleared out the registry and reinstalled after that also no avail.