had the same problem, and after finding out that i don't get help nor a reply from the support, i searched for myself. what i found is that the usergroup permissions in the classifieds are set wrong.
in my case, supermoderators had cpadmin set to 1 (which is yes), and administrators had it set to 3 (which is nothing, because only 1 and 0, yes or no are existent)
so what you will have to do is probably the same then i had to do, go to you phpmyadmin, in the classifieds_usergroups table look for administrator and check if cpaccess is set to 1, if not, edit that field and set it to 1, save. done...
you might check if your superadministrator field is set to 1 too, set this to 0 unless you want grant you superadmin access to the admin cp...
once you set the admin to 1, you can change the permission inside the classifieds admin cp though...
hope this helps, and sorry for my english
