If you hadn't changed avatars in the last few months, you may need to re-upload it through the new image system.
You can set your avatar via: http://www.zam.com/user.html?1#Forum_and_Comment_Settings
If you don't have a copy of your old avatar anymore, and it was under the old system, you can still download a copy from here: http://www.zam.com/imgul.html
After you upload the avatar, you need to click on it's icon in the list of avatars to set it as current, here: http://www.zam.com/user.html?1#Forum_and_Comment_Settings