Google Sandbox ok, Live "Whoops! Your session has expired"

I have done a bunch of testing of my store in sandbox mode with Google Checkout and it has all worked fine.

Today I turned the store on to live mode and reconfigured my version 1.47 Google Checkout to go to their live system.

I ran an order through the live system. It connected to Google Checkout just fine and accepted my payment. However when I try to go back to my Zen Cart store (version 1.9h) I am presented with "Whoops! Your session has expired error" and the order never shows up in ZenCart.

I verified that my callback URL and assorted settings are identical in my sandbox versus real Google checkout account yet I still have this issue.

I flipped the add on back to sanbox mode, ran another sale through it and it processed correctly.

Anyone have some advice on where to look for the source of the problem? Many thanks.

I managed to correct the problem. My site uses the .htaccess Basic Authentication Mode set to TRUE.

To fix the error I regenerated the .htaccess / .htpassword pair

Afterwards I was able to process orders in both the sandbox and production environment.