The error 1320 is shown when the country that has been specified as parameter is not yet correctly configured in the admin of the application.
You can find the setting in Admin > Delivery Settings. Click the € icon in front of the "international home or office" option.
Next, click on the "Add price zone" button.
In the new screen, you are able to select the available countries for the zone. For each weight class a price needs to be entered. It is possible to create multiple price zones.
Afterwards, don't forget to save your configuration as well or your changes won't be applied.