I debugged how the addon handles the call back from NAB Transact. I noticed the code in init_session.php (kind of) ignores the callback if the call back URL is not SSL.
The following fix might solve the issue:
Find the following 2 lines in /includes/modules/payment/nab_transact_hpp.php
PHP Code:
$gateway_vars['return_link_url'] = zen_href_link(FILENAME_CHECKOUT_SUCCESS, '', 'NONSSL', true);
$gateway_vars['reply_link_url'] = zen_href_link(FILENAME_CHECKOUT_PROCESS, $query_string);
Replace them with
PHP Code:
$gateway_vars['return_link_url'] = zen_href_link(FILENAME_CHECKOUT_SUCCESS, '', (ENABLE_SSL ? 'SSL' : 'NONSSL'), true);
$gateway_vars['reply_link_url'] = zen_href_link(FILENAME_CHECKOUT_PROCESS, $query_string, (ENABLE_SSL ? 'SSL' : 'NONSSL'));
This will ensure NAB Transact will call back a SSL URL. This should solve the problem.
The catch is, your cart must have SSL Certificate installed.
I am at a loss to explain how this problem cropped up all of a sudden. Did you change the version of the cart when you moved the store?
Please post back if this solves your problem