Error: What does 'Shipping Country Code / State Code is not unique.' mean?

Are you getting the following error when trying to setup shipping?

Error from server: Shipping Country Code / State Code is not unique. The field: "countryCode" errored because "Country Code is not unique" .The field: "stateCode" errored because "State Code is not unique" .

This error comes up when you are trying to add a State in more than one shipping zone. You can only have a State in one shipping zone (ie. California can not exist in Shipping Zone 1 and Shipping Zone 2).

We recommend reviewing the selected States in each shipping zone to determine the State that is duplicated.

For additional information on how to setup shipping, please review the documentation on Setting up Shipping in Commerce7.