4xx : Client Error

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Return codes within the 400 range indicate problems with the browser or the machine on which it was started.

400 Bad Request:

This code generally means that the requesting URL is bad or the server did not understand the request.

401 Unauthorized:

Generally means that a username/password or some other form of authentication needs to occur.

402 Payment Required:

This code is not currently used.

403 Forbidden:

Accessing the requested URL is not allowed.

404 Not Found:

Your browser cannot locate the document corresponding to the URL you entered. An improperly typed URL is usually the cause.

405 Method Not Allowed:

This usually means that the page is trying to run a script that isn't allowed.

406 Not Acceptable:

Content that the browser can not accept. Such as: when flash content is downloaded but the the flash plugin isn't installed.

407 Proxy Server Authentication Required:

A proxy server is in use and to properly access this server, authentication must occur.

408 Request Timeout:

This generally denotes a slow server or a server that is overloaded. Try the URL a bit later to see if its just server load.

409 Conflict:

This is vague but this occurs when the attemp to alter a resource is unsuccessfus.

410 Gone:

This is vague but this occurs when the attemp to alter a resource is unsuccessful.

411 Length Required:

This occurs when the server requires the content-length parameter to be set.

412 Precondition Failed:

This response code allows the client to place preconditions on the current resource meta information (header field data) and thus prevent the requested method from being applied to a resource other than the one intended.

413 Request Entity Too Large:

The server is refusing to process a request because the request entity is larger than the server is willing or able to process. The server MAY close the connection to prevent the client from continuing the request.

414 Request-URL Too Long:

This rare condition is only likely to occur when a client has improperly converted a POST request to a GET request with long query information, or when the client/browser has been caught recursive URL redirection.

415 Unsupported Media Type:

There may have been an error in the MIME type indicated in the request header, i.e., your browser might have requested an image file, when in fact the requested file is an application.

416 Requested Range Not Satisfiable:

This occurs when the browser requests data that is larger than the max amount able to be received per request.

417 Expectation Failed:

This occurs when the server isn't able to perform the expected server action as set by the client/browser.