From what I've heard, the forum's server (or whatever the proper jargon is, not really a tech guy) recently has really been not liking it when you change your avatar after the first time. But, always make sure your image is 75x75, as small as possible (as in compression), and try every typical file type (.png, .jpg., .gif., etc.). Animated gifs are also harder to make your avatar because they're usually larger than regular files.
If it helps, your current avatar is a shiny zoura in its idle animation. Sometimes your computer forgets to update its cache (again, i think this is the wrong jargon but i'm trying) and unless you refresh your current page, it stays the same.
Can we also see a picture of your new avatar?