I just extended a Web Application and provided it a new URL and host name. After completion (and altering my host file to direct the new url) I can see the new web sites created in IIS on each of the servers but cannot navigate to it.
This error (HTTP 404 Not Found) means that Internet Explorer was able to connect to the website, but the page you wanted was not found. It's possible that the webpage is temporarily unavailable. Alternatively, the website might have changed or removed the webpage.