The changing of avatars was disabled due to a hack that exploited weaknesses in the security of avatars. Then when the uploading of avatars was reenabled the forum was DDoS'ed within hours of when the April fools joke regarding the avatars was suppose to expire, allowing avatars to work "properly".
It should be obvious as to what happened.
But Avatars are still enabled. I don't think this was the issue else Theymos would have again disabled it after the attack.