Hehe, Avast, Avira, AVG… I use all three free versions on one computer or other (not for myself ) and haven’t had this kind of problem with either.
Avast: running ~2 years on XP, only negative is that you need to re-register each year (and have to merge the two! system tray icons).
Avira: <1 year on XP, annoying nag screen (can be circumvented) and often very slow to make connection with update server.
AVG: ~1 year on XP and Vista, trouble-free. Advertises itself in your e-mails by default, which is kind of nifty.