Problem solved - the validation system makes silly assumptions and for example, expects all addresses (for address 1) to start with a number. Even though our address has no numbers (as per the national post office and national postcode authorities - I double checked), I added a unmber ("1") and the form correctly submitted. This may (or may not) work for you, but worth a try.

Another warning: the way the error is reported pointed to an issue with the postcode (Eircode for us) when in fact the issue was with Address Line 1. Good luck.

To VMWare: our addresses are not incorrect/incomplete, the address validation system is just broken for certain countries.