The form builder css was referencing Spry classes that are no longer used.
I have fixed it in the extension. If you download and install the latest version, it should create the correct code now.
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.