Browser Error Codes
Reported errors involving your browser's operation.
The most common is the 404 error (unable to connect to a Web page) which can mean that the address in no longer valid, you used the wrong address (especially when using FTP), or the site is temporary down or overwhelmed with traffic.
It is a good idea to create 404 error page which comes up and offers the user other links to your Web site in case the page they wanted is unavailable.