Authorize.net not working

(Sorry... this was meant for EVENT BOOKING forum thread).

We use a 3rd party for authorize.net. When we upgraded from an older version of event booking to this new one, it stopped working. They told us to put this in as the url in this file: AIMGateway.php

Replace

'liveEndpoint' => ' secure2.authorize.net/gateway/transact.dll ',
with
'liveEndpoint' => ' www.iatspayments.com/netgate/AEGateway.aspx ',

Is there another place in any files that I should edit? I can't get this to work. It just keeps telling me invalid response from payment gateway... but it's definitely the correct info and api key / password

Thanks!