You show a missing function from Marco's version of Zen Cart but you are showing an image from a different version of Zen Cart ...

You need to see if you have mixed up the files and what is actually installed for USPS on your server ...

Make sure that you have no backup or renamed files on the shipping modules in the directory:
/includes/modules/shipping

and that the files in the directory:
/includes/modules/shipping

are the code files and the files in the language directory:
/includes/languages/english/modules/shipping

are the language files ...