I had a customer from Lancashire, UK get stuck today, because my Zones shipping module was saying no shipping to him. Lancashire was in the state field, as it's a "county" in the U.K.

I added the 78 or so counties to the zones table, using http://www.oscommerce.com/community/contributions,925

and was still having the problem.

UK was in Zone 3 of my country list.

The solution was that the country code for the UK is GB, not UK. I changed that in the shipping module, and that alleviated it.

I hope that maybe this will help someone else find what can be a frustrating error.