unable to use USPS

I’m using WP e-Commerce and for some reason, not apparent to me, I’m not able to use the USPS service because the password sign in is absent from the shipping module – settings>store>shipping>shipping module>usps. I just asks for a uspsID which I’m told by USPS should include a user name and a password but alas only one space is available to fill in.
I’m using WP version 3.4.2 WP e-Commerce version 3.8.9
I know there must be something very obvious that I have missied due to exhaustion.

Any help would be greatly appreciated