Web tech comments: Please also put this to the vb.org thread..
Here is sample of one of the avatars' file name.
The record on their profile is avatar41635_4.gif, but when I checked the directory, the correct name is avatar41635_3.gif
The number after the _ is the avatarrevision column from the 'user' table, and it should get incremented whenever a user uploads a new custom avatar. So you could fix the problem for a user by changing avatarrevision or the actual file name, but I don't know why they would get out of sync. There may be some other problem with uploading custom avatars. Maybe check the permissions on the avatar directories.