I have tried many solutions with no luck until...
I am using merchantplus as my gateway which is compatible with authorize.net.
What I did was create a new .php file using all the same code as ps_authorize.php and a new ps_authorize.cfg.php file and renamed them ps_merchantplus.php and ps_merchantplus.cfg.php
Then I went into the files an changed the "AN" throughout the file and also in the .cfg file to "MP".
Then added a new payment method and used the MP and the new ps_merchantplus.php file.
I also had to change the secure.authorize.net to my gate way gateway.merchantplus.com and the rest of the posting url to /cgi-bin/PAWebClient.cgi instead of the default authorize.net code.
This would not work until I remade the files. So I think it is most likely a database problem with the "AN" for some reason.
Before the file change this would not work, now with the change it successfully posts to my gateway. My only problem now is that the CVV and AVS are not working properly. I am not sure if it is a problem with VM or on my gateway side. If I use the testing codes it will verify just fine, but if I use a real card and CVV codes they fail on my gateway side. So I am thinking it is on my gateway side. Still waiting on help from Merchant Plus.
Hope this can help others, because I tried everything else on this forum with no luck
Ihave evey thing working great now, my problem was a cache problem and setting up my gateway.