HTTP status codes, also known as HTTP error codes, are information provided by a web server to the user regarding the execution of a command. Each time a client sends a request to a web server, the latter provides an HTTP status code, thus communicating to the user whether the request was processed successfully or not.
There are several types of HTTP status codes: information codes (100), confirmation codes (200), redirect codes (300), client error codes (400), and server error codes (500). In our FAQ we will examine the last two types.
Client Error HTTP Status Codes are displayed when the client sends a syntactically incorrect request that cannot be processed by the server. Only the user can intervene to remedy the error by sending a new request.
400 - Bad Request: The server does not recognize as valid the flood of data sent by the client, the web browser or our CheckUpDown robot, because it does not fully respect the HTTP protocol.
Possibile Solutions: Solving the bug inside the code on server side (for example ASP or PHP). If you are using .ASP the problem may occur because of the presence of Unicode characters: a .NET Framework update could be required.
401 - Authorization Required: It points out a problem of authentication: the page you're trying to enter requires a username or password that you've typed incorrectly.
Possible solutions: Recovering the valid access credentials (usually they depend on the website not on the hosting provider).
403 – Forbidden: This error can depend on the prohibition to explore the website's directory: it's an option that several portals automatically implement for security matters and, except in several occasions, it's not recommendable to modify it. Otherwise, you could compromise the stability of the website because every user could check any file or find out eventual exploit or execute a PHP/ASP files arbitrarily.
404 - Not Found: This error is extremely common when you change the address of a page or when the URL you're trying to connect is not reachable anymore (broken link).
Possible solutions: The first step is checking the address manually and try to restore it (the solutions may depend on the type of CMS, just in case ask to your webmaster). There are several WordPress plugins, such as Broken Link Checker, that can periodically detect these kind of errors (and correct them). It's also possible to detect all the broken links automatically, using free softwares such as Xenu (for PC) or Integrity (for Mac).
405 - Method Not Allowed: The server is not available to view the page using the method you requested. Possibile methods can be GET, PUT, POST, DELETE and many more.
Possible solutions: The standard method used by all servers is PUT, so, this error should never occur: otherwise, contact our tech support.
406 - Not Acceptable (encoding): This error points out the status coming back from the server, in case the HTTP request owns Accept's headers not compatible with the content of the request or that the server cannot manage.
Possible solutions: The diagnosis can be quite complex. We suggest you to contact our tech support.
407 - Proxy Authentication Required:The connection to the website is allowed only using proxy.
Possibile solutions: Connecting using a proxy server.
408 - Request Timed Out. The request you sent to the website server (for example, a request to load a web page) took longer than the website's server was prepared to wait.
Possibile solutions: We suggest you to check the Microsoft dedicated guide or contact our tech support.
409 - Conflicting Request. The request could not be completed due to a conflict with the current state of the target resource.
Possible solutions: We suggest you to check the Microsoft dedicated guide or to contact our tech support.
410 – Gone: The page requested is no longer available on the address you typed (error 404 "definitive").
Possible solutions: Contacting your webmaster for the new address.
411 - Content Length Required: The server refuses to answer because the request does not include informations about dimension.
Possibile solutions: Contacting our tech support or the webmaster.
412 - Precondition Failed: The VPN client software detected that the server does not respond anymore and removed the connection.
Possible solutions: Contacting our tech support.
413 - Request Entity Too Large. The request made from a client is too large to be processed by the web server.
Possibile solutions: Clearing your browser's cache and try to load the page again.
414 - Request URI Too Long. The URI requested by the client is longer than the server is willing to interpret.
Possible solutions: Ask the webmaster to use shorter URL.
415 - Unsupported Media Type. Part of the request sent to server is not supported for a matter of format.
Possibile solutions: Contacting our tech support.
Another class is the Server Error HTTP Status Codes displayed when the server encounters an unexpected internal problem that prevents it from processing the request. In this case the client has sent the request successfully but the server is unable to process it.
500 - Internal Server Error: Generic error message.
Possible solutions: It's one of the most difficult error to detect: in the WordPress case, for example, can represent a typing error inside the .htaccess configuration file (to check and eventually correct). Checking the log of the server can be very useful for a deeper comprehension.
501 - Not Implemented 501: The request processed by the browser uses a method out of the HTTP standard and not implemented on server side. This may occur if a request is not processed by a common browser but by a dedicated software.
Possible solutions: Checking the request operated by the software and modifying it.
502 - Bad Gateway: This error may be the consequence of an IP communication problem between back-end computers, including the web server of the website you are trying to visit.
Possible solutions: Clearing your browser's cache and trying to load the page again.
503 - Service Unavailable: Service generically not available.
Possibile solutions: Clearing your browser's cache and trying to load the page again.
504 - Gateway Timeout: The gateway didn't respond in the expected time because of several motivations.
Possible solutions: Clearing your browser's cache and trying to load the page again.
505 - HTTP Version Not Supported: The server does not support, or refuses to support, the major version of HTTP that was used in the request message. It may occur with very old implementations of the server or with experimental versions of the browser. It may be the consequence of a syntax error if the request has been written manually.
Possibile solutions: Checking the syntax of the HPPT request and the web server version.
