There are numerous other possibilities.
to troubleshoot, open the bindings panel and Expand the USPS binding group and add the Error bindings to your page, this will tell the error being returned by USPS.
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.