The cart has been working perfectly for 2 years, but for the last few weeks it has started showing an error immediately after checkout.
The order still gets placed correctly, but there is a white screen with the following error message :
Internal Server Error The server encountered an internal error or misconfiguration and was unable to complete your request. Please contact the server administrator, firstname.lastname@example.org and inform them of the time the error occurred, and anything you might have done that may have caused the error. More information about this error may be available in the server error log. Additionally, a 404 Not Found error was encountered while trying to use an ErrorDocument to handle the request.
Please help urgently, as customers are being scared away.