Maybe vB5 has changed their avatar API and that's causing the display to fail. Does it link to the correct user profiles? I don't have my vB5 test forum at the moment, so I don't recall if the avatars originally linked to member profiles.
This product hasn't been tested on the 5.3.x branch of vB5 yet so issues may occur when updating vB5 - they place no value on backwards compatibility for 3rd party developers (or rather, they place no value on 3rd party developers at all).