On your 155 site, are you using the latest version of the AIM module, which removes the MD5 stuff?

Module: https://github.com/zencart/zencart/r...izenet_aim.php
Lang file: https://github.com/zencart/zencart/r...izenet_aim.php

The setup instructions were updated to remove the MD5 part: https://www.zen-cart.com/content.php...payment-module