What are error pages?
Error pages are the result of an HTTP status code. This status code is the server's response - a three-digit code - to your browser's request. This means that when you enter a site's URL in the browser, it sends a request to the server. It receives a code - an HTTP status code.
Status codes are divided into classes and subclasses depending on the number it starts with, from 1 to 5. Each class represents different types of responses, for example:
1xx: informational responses - request accepted and understood
2xx: success - the request was successfully completed
3xx: redirect - you have been redirected to another page
4xx: Client Errors - The requested page could not be found or accessed
5xx: Server Errors - The server was unable to complete the request
The following is a complete list of client and server error messages:
4xx - client error
A client error is an error that occurs on the user's computer.
400 - Bad request.
401 - Unauthorized.
401.1 - Login failed.
401.2 - Login failed due to server configuration.
401.3 - Unauthorized due to an ACL on the resource.
401.4 - Filter authorization failed.
401.5 - ISAPI/CGI application authorization failed.
401.7 - Access denied by URL authorization policy on the web server. This error code is specific to IIS 6.0.
403 - Forbidden. IIS defines a number of different 403 errors that indicate a more specific reason for the error:
403.1 - Execute Access Denied.
403.2 - Read access denied.
403.3 - Write access denied.
403.7 - Client certificate required.
403.8 - Site access denied.
403.9 - Too many users.
403.10 - Invalid configuration.
403.11 - Change password.
403.12 - Mapper denied access.
403.13 - Client certificate revoked.
403.14 - Directory list rejected.
403.15 - Client access licenses exceeded.
403.16 - The client certificate is untrusted or invalid.
403.17 - The client certificate has expired or is not yet valid.
403.18 - Cannot execute the requested URL in the current application pool.
403.19 - Cannot execute CGI for a client in this application pool.
403.20 - Passport login failed.
404 - Not Found.
404.0 - File or directory not found.
404.1 - The website is not available on the requested port.
405 - The HTTP verb used to access this page is not allowed.
406 - The client browser does not accept the MIME type of the requested page.
407 Proxy authentication required.
412 - Precondition not met.
413 - The request object is too large.
414 - Request-URI is too long.
415 - Unsupported media type.
416 - The requested range is not satisfied.
417 - Runtime error.
423 - Blocking error.
More about some:
The 400 error code refers to a browser issue. This occurs when a message is identified as corrupted and the request that the server receives cannot respond with the correct information requested.
This type of error is caused by missing login credentials because you are not authorized to access the page. This server is reporting that you are not authenticated or that you have mistyped your username or password.
This is something the user can deal with in a few easy steps - sometimes it just needs to clear the browser's cache and then a trusty old refresh of the selected page.
The error appears due to the fact that you do not have the necessary rights to access the page you are looking for. The 403 response comes after the 401 response - when the user is logged in but not authorized to access the desired resource.
Double check your file permissions, clear your browser cache, reload the page, contact your system administrator.
This error means that the server could not find the requested page. This is an indicator that the page is not working properly and needs to be fixed.
Check if you entered the URL correctly, reload the page.
Unlike other error codes, this is a timeout code that the user could cause to stop the request before the server received the information. This can also be an indicator of a slow server, so it's best to keep an eye on the server if this message appears.