That's weird. Since it disappeared from imageshack, I assume it isn't something on our end, but I'll definitely look into it! If you want, email me your avatar (or even just the link you're trying to use) and I'll see if I can get it back into your profile.
I checked your profile and see the no image button is marked. I do know our security system checks avatars and keeps possibly malicious ones off - not sure if it automatically checks the no image button if the avatar image is corrupt...
If your image was corrupted, that might explain how it disappeared from imageshack, too.