404 Page Not Found local or shared file [closed]

So I downloaded a zip file here https://archive.org/details/RAVEN1NET containing the web pages of a no longer active website. Upon opening the .html files it gives a “404 Page Not Found local or shared file” error saying on the page: “PAGE NOT FOUND
We cannot locate the page you’re looking for. Please check the address and make sure all letters are lowercased with no spaces. You may also move to a different page by using the links in the menu bar above.” Why does it say this for the .html files and not the .htm files which open the webpages?