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404 errors are common errors indicating that the browser was able to communicate with the server, but the server could not find what was requested, leading to the page not loading.
The error usually occurs when a user clicks on a broken link, or a link that no longer leads to an active page.
Additionally, the error occurs by user error, such as typing the URL incorrectly.
Sites can choose to display custom 404 error pages, with custom graphics or flash.
The 404 is the error code produced by the Web server and it is recognized by search engines, which use it to remove broken links from indexes.