If you are receiving this error message please check the Country Code you are trying to synchronise is in the list of country codes within Dimensions. If it does not exist please create the code in Dimensions and re-synchronise the Customer.
If the Country Code does exist, but is set incorrectly on the customer record in Dimensions, and if the customer code has no transactions against it, you can change it in Dimensions by navigating to:
Click Debtors, Records, Customers
Find and select the required customer
Click Edit.
Select and change the drop-down containing either GB VAT, EU State or Non-EU State.
If required, enter the country information.
If the record has already been used, create a new customer with the correct country code, and make the old one inactive.