I too am encountering this problem, it was fine until a week or so ago, and then it stopped working completely. I have turned off all non-essential programs loading at start-up and it still does not work.
I am running Vista Ultimate and NOD32 (but have never had a problem until recently)
Any further suggestions? FYI I have uninstalled both MSN and Pessenger Plus and then reinstalled them again with the same result, when M+ is installed it starts MSN but shows as not loaded
M+ version is 4.23.0.276 and Messenger is 8.1 (8.1.0178.00)
Please help I miss the scripts and tabbed chats (tabbed chats especially as I use this feature a lot)