We recently started experiencing 500 Errors (Internal Server error) on the Thankyou.cgi script when a user presses Submit Order to commit the order. The problem only happens when a credit card is used and does not happen if the user uses PayPal payment method. The email confirmations are sent and the order is recorded, the only issue is that the page redirect to the 500 Error is causing user confusion and might indicate some other problem we haven't yet discovered. We are on Shopsite 12.3.
Has anyone experienced this issue? Any ideas on what things we might check? My sense is that this may be a payment gateway issue.
Thanks in advance.