hi - i dont know if i know the issue, but a quick thought was if you are using USA as the country code or US. i got tripped up on this one time and it does cause orders to fail.
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.