The error is on a page on my site that is called from Authorize.net's designated response/receipt page via a form action.
Yes, I'm trying to integrate eCart with an existing system that was set up with some template system. I'm wondering if that may even be possible now. What would I do if I wanted to just use the eCart pages? The key seems to be Authorize.net's Response/Receipt URLs. Which page(s) should I set that URL to for eCart to complete the order?