Authorize.net Module Error

[Eurcynia]

I have been receiving an error on checkout when I use the Authorize.net module and I'm not sure if its something with OSC or something with Authorize.net. I have tried test mode, production mode, my transaction key to password and back, but i still get the same error at the very end when you click to confirm the order:

 

 

It goes to https://secure.authorize.net/gateway/transact.dll and throws the following 404:

 

 

Not Found

The requested URL /checkout03.asp was not found on this server.

 

Additionally, a 404 Not Found error was encountered while trying to use an ErrorDocument to handle the request.

 

Is it looking for this file on my server even though the URL is authorize?

 

Thanks for your help!