Looks like not only I have a problem with Authorize.net AIM.
I studies this forum thread completely as well and did not find an answer.
Thank you for replying and helping me.
Authorize.net AIM module.
First thing I did I made the changes described in the installation manual for the Protx module to the already installed and working Authorize.net AIM module but it didn't made it work.
Then I tested 2 more different contributions of available authorize.net aim modules offered on the oscommerce site, non of them worked.(with or without changes as for protx).
With OPC 1.4 they just alert'ed an error when module was selected, with 1.3 it loaded names of the fields with an php error that an argument is null in str_replace or so in the confirmation(...) function of the module.
I tried stock version of A.net AIM which is in osC by default - fields loaded, cc info may be entered but the card cannot be processed, even without OPC it doesn't worked.
Then I tried to combine stock and latest modules of A.net AIM swapping functions from new module to the stock one
( My idea was that if I will change the function that establishes the connection with authorize.net test or secure server and sends there data it will work.) This way I made fields appear and module to load but the transaction was unsuccessful anyways.
I posted a project on freelance website and asked for 2 php coders to help me. They assured me that they will help me in 2-3 days but none of them contacted me back in a week and a half, so I don't want to relay on somebody else.
I want to fix it on my own, I know that there are people who HAVE that module working and would be more that grateful if they will direct me or provide with the changes that need to be made.
I don't have any changes made to the checkout of the website, except fully working new Authorize.net AIM module and OPC installed and disabled.
Also I installed 3 different checkout-improving contributions on my test servers.
FEC doesn't provide features needed,
AJAX checkout doesn't work with the payments
Single page checkout was too messy and not working with payments as well and not supported anymore. (Although Thanks steve_s for good contribution made; by his advice i decided to work with OPC)
So I hope someone will help me with this one!