This is a long standing problem with the boards , Not to sure what the problem is but you could try uploading the avatar then log out of the forum , clear your webcache then log back into the forum , No guarantees but that has worked for me in the past .
Hmmm , What format is your Avatar ? It needs to be in JPG format and its case sensitive for some reason
I tried getting .jpg to work but all I got where errors , In the end I just renamed it avatar.JPG on my host and it worked
Paul
[Edited on 6-4-2006 by Screwy]