I seem to get the same error message when trying to UPLOAD an avatar on the forum's website.
I tried to upload the avatar over my FTP server, and just point out the link, and it worked. You can try that, and make sure your avatar meets the required size (80X80X15KB)
Still, have no idea why are we experiencing that error, I'm just showing out an alternative.
No, seems it won't work. There are no errors when pointing out the link, just that the script isn't copying the image from the web, and you get to have no avatar.
Perhaps one of the galleries would help?