I'd have to debug with FTP access to be sure, but it is possible that it is a bad php.ini setting for the session_save_path variable preventing session variables from being stored.
Your friends over here at WebAssist! These Dreamweaver extensions will assist you in building unlimited, custom websites.
These out-of-the-box solutions provide you proven, tested applications that can be up and running now. Build a store, a gallery, or a web-based email solution.