If you get the following error:
[email protected] has sent Google a shopping cart with errors in it. We'll contact them to ask that they fix this problem. As this could be a temporary issue, you can go back in your browser to try checking out again.
Take a look in the Integration Console for a more detailed description of what's gone wrong. Log into http://sandbox.google.com/checkout/sell then go to Tools > Integration Console.
In my case I found the following error:
The currency used in the cart must match the currency of the seller account. You supplied a cart with GBP and the seller account is associated with USD.
This is a companion discussion topic for the original entry at https://our.umbraco.com/forum/7189-xxxx-has-sent-google-a-shopping-cart-with-errors-in-it