You could use file_exists() to check if the file exists instead of using a session variable. Upload a copy of the page you are working on and I can be more specific with my help.
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.