Avatars have to meet certain requirements.
They must be smaller than 100x100 pixels.
I think there's also a file size limit. Something like 10k. But I'm not sure. And, looking at some of the larger avatars, it may not be there anymore. (Looking around, I see a couple of avatars over 20k which show up fine...)
And, of course, the avatar must be available on the web somewhere, and viewable by external link (many sites don't allow hotlinking, since it sucks up bandwidth, especially without properly crediting the site).
If you're having trouble with your avatar, it's probably one of those three things. So, check the size first (image properties should give you pixel size and file size), then take a look at where it's stored.
Hope this helps.
Paul
