Well, obviously just delete some people you don't know, or never go on, then add more people, kinda like xbox live friends list.
I heard this works really good too, last time I had a problem I did this and my computer was running really fast, and download speeds were just crashing, literally
"I hate to advocate drugs, alcohol, violence, or insanity to anyone, but they've always worked for me."
- Hunter S Thompson
Try to reinstall or go to another pc
REINSTALL TIME NIGGA
@Boombox just re install it
Sometimes when that happens your msn may or may not be full,like if u delete 1 person you'll be able to add 2.