http://www.allfordmustangs.com/revie...t-sidebar.tmpl
Your template shows the call to it so if you say its on then it should display and it does in every reviewpost I see.
http://www.allfordmustangs.com/revie...onlinepal.tmpl
The template is there and looks fine so then your issue is your $whosonline is empty so then why is this. If you view the iponline table using phpmyadmin what is in there?
Try reuploading all the files except config files.