Avast! Won't Update

Hey guys, I’ve been experiencing this problem for about a week now. I am a student at a university and the university required me to install avast to connect to their internet. They are now blocking me from using their internet because my definitions aren’t updated, however when I try to update it, I get an error telling me that I cannot connect to the servers (or something along those lines). I am running Mac OS X 10.6.8. Anybody in a similar situation? Anybody have any ideas about how to fix this?