This error occurs because the interface is looking at the Supplier record Country Code, which appears to be invalid. To check this:
On the Toolbar, click Purchase Ledger, Suppliers.
Find and select the Supplier named in the Exception Log.
Click the Supplier tab.
On the left, in the Country Code section, if this area is populated, click the ellipses (...) icon.
The Country Code may have been removed from the list and needs to be added again.
Alternatively, remove the Country Code and replace it with a valid one.