ZC Version: 1.3.9h. Install is the Dreamhost one-click install.

A client of mine has a store that uses per-item shipping. It has one set of prices for the US Zone and one set for the International Zone.

When I do a test order, if I enter an international address (I tested Canada) it works fine. If I enter a US address it gives the error: "Sorry, we are not shipping to your region at this time.".

I've checked and the module seems to be installed and configured correctly, and it works just fine for international addresses. (The FAQ says this error occurs when your shipping module isn't installed correctly, or the user enters an address in a zone that isn't valid. But this is just the United States zone and I've tried about a dozen valid US addresses.)

You can test the store at: https://cordobaszekely.com/store
Create a cart and go the second step of checkout to see the problem.

CHANGES BEFORE THE PROBLEM OCCURRED. We haven't changed anything related to shipping lately. The only thing that has changed recently is that the client's Authorize.net account expired and I have installed the API credentials for their new Authorize.net account.