What do the error codes mean?

The following article discusses the meaning of error codes that may appear in your browser window. When a problem occurs loading a webpage, an error code and message will appear in the browser instead of the webpage. The error code and message that appears is determined by the type of error. Typically the error code consists of a 3 to 4 digit number and a brief message describing the error. Below, you will find a list of the common error codes and some suggestions for resolving them.

Note: To see the error code and message, it may be necessary to uncheck Show friendly HTTP error messages in your browser. This is usually found under Tools -> Internet Options -> Advanced.

The following is a description of the most common error messages:

Code Message Description
404 Page Not Found This error message occurs when the page that is requested does not exist on the server. This can occur if the user mistypes the name of the page, or attempts to load a page that no longer exists. One solution is to create a custom 404 error page that provides the user more detailed information and navigation so they can continue browsing your website. Instructions for configuring a custom 404 error page for a Windows account can be found here. Instructions for a Linux account can be found here.
500 Internal Server Error This error message occurs when the server fails to process a script that is being run. The error message will typically contain information relating to the script failure. The resolution to this type of error will be based around the additional information provided in the error message. If you do not see additional information, please ensure that Show friendly HTTP error messages is unchecked.

The following is a complete list of client and server error messages:

4xx – Client Error
A client error is one that occurs on the users computer. For example, the user may request a page that does not exist, or the user may not provide valid authentication information.

Code Message
400 Bad request.
401 Access denied. IIS defines a number of different 401 errors that indicate a more specific cause of the error. These specific error codes are displayed in the browser but are not displayed in the IIS log:
401.1 Logon failed.
401.2 Logon failed due to server configuration.
401.3 Unauthorized due to ACL on resource.
401.4 Authorization failed by filter.
401.5 Authorization failed by ISAPI/CGI application.
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 cause of the error:
403.1 Execute access forbidden.
403.2 Read access forbidden.
403.3 Write access forbidden.
403.4 SSL required.
403.5 SSL 128 required.
403.6 IP address rejected.
403.7 Client certificate required.
403.8 Site access denied.
403.9 Too many users.
403.10 Invalid configuration.
403.11 Password change.
403.12 Mapper denied access.
403.13 Client certificate revoked.
403.14 Directory listing denied.
403.15 Client Access Licenses exceeded.
403.16 Client certificate is untrusted or invalid.
403.17 Client certificate has expired or is not yet valid.
403.18 Cannot execute requested URL in the current application pool. This error code is specific to IIS 6.0.
403.19 Cannot execute CGIs for the client in this application pool. This error code is specific to IIS 6.0.
403.20 Passport logon failed. This error code is specific to IIS 6.0.
404 Not found.
404.0 (None) – File or directory not found.
404.1 Web site not accessible on the requested port.
404.2 Web service extension lockdown policy prevents this request.
404.3 MIME map policy prevents this request.
405 HTTP verb used to access this page is not allowed (method not allowed.)
406 Client browser does not accept the MIME type of the requested page.
407 Proxy authentication required.
412 Precondition failed.
413 Request entity too large.
414 Request-URI too long.
415 Unsupported media type.
416 Requested range not satisfiable.
417 Execution failed.
423 Locked error.

5xx – Server Error

A server error is one that occurs on the server when the page is requested in a browser. The server cannot complete the request because it encounters an error.

Code Message
500 Internal server error.
500.12 Application is busy restarting on the Web server.
500.13 Web server is too busy.
500.15 Direct requests for Global.asa are not allowed.
500.16 UNC authorization credentials incorrect. This error code is specific to IIS 6.0.
500.18 URL authorization store cannot be opened. This error code is specific to IIS 6.0.
500.100 Internal ASP error.
501 Header values specify a configuration that is not implemented.
502 Web server received an invalid response while acting as a gateway or proxy.
502.1 CGI application timeout.
502.2 Error in CGI application.
503 Service unavailable. This error code is specific to IIS 6.0.
504 Gateway timeout.
505 HTTP version not supported.

Additional information about less common error codes and messages can be found on Microsoft’s website.

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