Google Checkout - order notification failing

I am getting errors from Google saying that it can’t notify my cart of the checkout process.



What API version should I be using inside my Google Checkout Account? Currently I am using 2.5, should this be one of the lower ones?



My company will only post digitally signed carts is Checked



I am using [url]https://www.example.com/products/payments/google_checkout_response.php[/url]



Notification is set to XML



And the Notification Filtering is UNchecked.



Inside of CS-Cart my settings are



The I Accept is Checked

My Merchant ID and Key are set and verified against Google and correct.

US Dollar

Live Mode

And no default values for shipping.



The error I am getting from Google says


[QUOTE]We encountered an error processing your notification acknowledgment. The error we got is: Expected serial number was not contained in notification acknowledgment. [/QUOTE]



The XML they received

[HTML]<?xml version="1.0" encoding="UTF-8"?>[/HTML]



And the XML they sent is a huge long thing with lots of information inside of it.



If I can provide you more information, just let me know. I think I have version 2.1 of CS-Cart, let me know where I can check on this and I can verify, but I downloaded it from here just a couple of weeks ago as a trial thing.



Thanks!

Can anyone help me with this issue?