It has recently been noticed that if someone chooses a remotely hosted avatar, the forum software does not apply dimension and file size restrictions as it does with uploaded avatars. For this reason, remote avatars have now been disabled.
You can still have an avatar, but you will need to...
Some of you have already noticed that avatars aren't uploading to the forum. I'll have a look at this.
In the meantime, you can get them working by hosting them elsewhere and using the 'Link to off-site Avatar:' option in your profile. :)