This has to be one of the most irritating issues I've come across in some time. Using any of the Authorize.net AIM modules for osCommerce 2.2 the customer would consistently be sent back to the Payment Details page with an error:
There has been an error processing your credit card
It seems that many people have been having this issue and there are many different possible solutions to the problem. The solution to this problem was found in this post: http://forums.oscommerce.com/index.php?showtopic=293398&pid=1309060&start=&st=#entry1309060
Basically, the MD5 Hash needs to be 80 bits and not 128 bits. I generated the MD5 hash as I normally do and pasted it into Authorize.net without realizing that the text was truncated and only the first 20 characters of my hash was actually stored. Authorize.net does not display this hash so you won't ever notice it in there. This is a VERY simple fix that has given me a headache for a couple of days. Hope this is helpful to someone.
