The error means that the php server is not properly configured to manage session variables.
it is most likely an issue with the session.save_path setting in the php.ini file.
you should contact your host to have them correct the problem.
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.