Execution got to
function _addresses_province_field_validate($form, &$form_state) {
in addresses.settings.inc:415
and gave the invalid error message.
I put in a couple of echos and found out that $form['country']['#value'] was empty.

The project I'm on is way too hot for me to spend more time on this now . . .
Jamming in
$form['country']['#value'] = 'us';
made it go for now.