I have been reading through this thread for days trying to find a solution for the problem I am having. Unfortunately, I have been unable to do so.

Every time an order is placed via Google Checkout no data is sent back to my administration section for the order. When I pull up the Intergration section of Google Checkout, I am presented with the following error:

Your server returned no data in its response; Checkout requires data of type merchant-calculation-results in response to merchant-calculation-callback
I have done a ton of searching through Google as well as this forums search functions and I cannot find anything that can help me tackle this problem. I have also contacted Google themselves and all they said was:

The merchant calculation callback is when Google Checkout sends information to your server regarding the address of the buyer so your server can calculate shipping costs, taxes, etc and return it to Google Checkout. Your server is not returning information in the reply to the merchant calculation callback.

It looks like you're using Zen Cart, please refer to the Zen Cart manual to correctly set up the merchant calculation callback for Google Checkout.
If anyone can help me out here, I would really appreciate it!

Thanks in advance!