The system has been running great for months now. Then all of the sudden just a few days ago, any user that subscribes to the site, makes it through the payment process. But aMember does not reflect that a payment has been made. The users account is stuck in "Pending" status. CCBill says that they are receiveing the info from aMember, but getting a 504 error on the "http://my-domain.com/amember/payment/ccbill/ipn".