I have a Magento 1.9 CE installation that was recently upgraded from 1.7. Authorize.net direct post worked in 1.7, but now it does not work. When I try to checkout, I get the standard message about "Response hash validation failed. Transaction declined."
I made a new hash key and entered it in both Magento and authorize.net. I then cleared the Magento cache. I still get this error though. I rebooted the server. I tried a different browser. Any thing I am missing?