I just contacted the USPS webtools help line.
they say it's a coding issue,, but it isnt on their end (because amazon uses the same server).
your admin need to email them at
[email protected]
let them know the XML string you are using, what server it is contacting, and what response you are getting back from them.
instructional help code cannot really be given over the phone.
( i dont do my website's admin or programming so i cannot help at this point)
if any one you get the answer before her, please post asap!