Los códigos de clase 4XX indican que has hecho algo mal. Concretamente, hay un error en el lado del cliente.
HTTP error 400 Bad Request
HTTP error 401 Unauthorized
HTTP error 402 Payment Required
HTTP error 403 Forbidden
HTTP error 404 Not Found
HTTP error 405 Method Not Allowed
HTTP error 406 Not Acceptable
HTTP error 407 Proxy Authentication Required
HTTP error 408 Request Timeout
HTTP error 409 Conflict
HTTP error 410 Gone
HTTP error 411 Length Required
HTTP error 412 Precondition Failed
HTTP error 413 Payload Too Large
HTTP error 414 Request-URI Too Long
HTTP error 415 Unsupported Media Type
HTTP error 416 Requested Range Not Satisfiable
HTTP error 417 Expectation Failed
HTTP error 418 I’m a teapot
HTTP error 419 Authentication Timeout
HTTP error 420
HTTP error 421 Misdirected Request
HTTP error 422 Unprocessable Entity
HTTP error 423 Locked
HTTP error 424 Failed Dependency
HTTP error 425 Too Early
HTTP error 426 Upgrade Required
HTTP error 428 Precondition Required
HTTP error 429 Too Many Requests
HTTP error 431 Request Header Fields Too Large
HTTP error 444 Connection Closed Without Response
HTTP error 449 Retry With
HTTP error 451 Unavailable For Legal Reasons
HTTP error 460
HTTP error 463
HTTP error 464
HTTP error 494 Request Header Too Large
HTTP error 495 SSL Certificate Error
HTTP error 496 SSL Certificate Required
HTTP error 497 HTTP Request Sent to HTTPS Port