Please help us to help you by reading and following the posting guidelines located in this thread: Please read before requesting assistance. The more information you give us the better we will be able to assist you. Thank you.HTTP 520 is not an osTicket error, its a webserver error. You should check your logs. You will also want to check your PHP error logs, and with your admin to see what they changed yesterday on your webserver.520 Unknown ErrorThe 520 error is used as a "catch-all response for when the origin server returns something unexpected", listing connection resets, large headers, and empty or invalid responses as common triggers.