Problems With Messenger Shutdown

Hello,

I have recently had some problems with MSN Messenger. Whenever I Shut Down
my computer, Windows XP goes through the shutting down the program thing with
the end now button, but it can't shut it down by itself. I have to click the
"End Now" button to get it to pass that point.

What could be causing this screen to come up? It hasn't come up in the
past, and it only happens on shutdown, not restart. Any ideas?

Thanks