I see the same as Sharla.
From the vBulletin site, here are a few of the board settings you might want to look at, but it is probably the second is different for admins than for users.
First, go through the options:
Overal usage of Avatars
Admin Control Panel > vBulletin Options > vBulletin Options
Here you can set the overal usage of avatars. If you want users to use avatars, turn it on here. If you want only certain usergroups to use avatars, still turn this on.
Custom Avatars
Admin Control Panel > Usergroups > Usergroup Manager > Edit Usergroup Permissions
Here you can set on a per usergroup basis the permissions to use custom avatars and if so, which sizes, etc. If you only want certain usergroups to use avatars, set their permissions to yes here so they can upload their own custom avatars.
Regular (Default) Avatars
Admin Control Panel > Avatars > Avatar Manager > Edit Avatar Permissions
Here you can edit the permissions for avatars per avatar category for usergroups. If you only want certain usergroups to use the default avatars (and only certain categories), you can set this here.
Hopefully that helps!