What are you using for your insert server behavior? You should be using dataassist and binding the file field to the "server file name" value in the bindings panel.
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.