the webassist/plugins/shopping_cart/checkout_form.php page is one of the power store files. you find it in the power store directory.
what is the error you are getting? i cannot troubleshot an error without knowing what it says.
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.