I cannot reproduce the problem with the current USPS January 2, 2011 C shipping module from post #26 ...
http://www.zen-cart.com/forum/showth...059#post978059

You may want to check that you have the correct file installed on the server ... and that you followed all of the instructions ...

One test is to go to the Tools ... Developers Tool Kit ... and in the bottom input box enter:
USPS GXG Envelopes

and select Catalog and click search ...

see what code comes up on the file on the server to ensure it matches the code in the New File ...