For anyone who works with the server, here is a list of the most common error codes:
301 - Moved permanently - The requested resource has been assigned a new permanent URI and any future references to this resource should use on of the returned URIs
302 - Found - The requested resource resides temporarily under a different URI.
304 - Not modified -
404 - Not found
500 - Internal server error -
503 - Service unavailable
12303 - The connection with the server was reset. It could be connection issue or firewall issue.