Edit includes/modules/payment/interac.php. Go to line 197. It says
Code:
$province_code_order = (in_array($order->billing['country']['iso_code_2'], array('CA', 'US')) ? zen_get_zone_code($order->billing['country']['id'], $order->billing['state'], '--') : '--');
change this to
Code:
$province_code_order = (in_array($order->billing['country']['iso_code_2'], array('CA', 'US')) ? zen_get_zone_code($order->billing['country']['id'], $order->billing['zone_id'], '--') : '--');
(So you change the last 'state' to 'zone_id') Retest.