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.
Either, the Country Code will have been removed from this list and it needs to be added again to be valid.
Or, the Country Code could be removed and replaced with a valid one.