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What is a 404 error? A 404 error is a frequently-seen status code that tells a Web user that a requested page is “Not found.” 404 errors and other status codes are part of the Web’s Hypertext Transfer Protocol (HTTP), written in 1992 by the Web’s inventor, Tim Berners-Lee. He took many of the status codes from the earlier Internet protocol for transferring files, the File Transfer Protocol (FTP).