INTERNET ERROR CODES !! Error 400 - Bad request. Error 401 - unauthorized request. Error 403 - forbidden. Error 404 - Not found. Error 500 -Internal error. Error 501 - Not Implemented Error 502 - Bad Gateway Error 503 -Service unavailable. Error 504 - Gateway Time-Out Error 505 - HTTP Version not supported/DNS Lookup Fail/ unknw host Error 500-599 - Server Errors.