Did you ever have USPS working for you?
Did you call USPS and have them Activate your account?
You are using the latest USPS and if you upgraded, you did save your settings and REMOVE and INSTALL the USPS Shipping module again, correct?
http://www.zen-cart.com/forum/showthread.php?t=80695
Note: the current version of Zen Cart is v1.3.8a ...
http://www.zen-cart.com/forum/showthread.php?t=81696



