look at the action on your form
the session will never be set because you are posting to a different page, move your session code onto that page and all will be fine.
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.