This usually happens when the cart include files are placed too low on the page, or if you name a recordset or other variable with the same name as the cart object. If you attach a copy of the page then I can take a look and be more precise.
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.