It means the system can't find what you are looking for even when it exists. I had to look it up, and this is Wikipedia's summary:
[Direct quote]:
"The HTTP 404, 404 Not Found, 404, 404 Error, Page Not Found, File Not Found, or Server Not Found error message is a Hypertext Transfer Protocol (HTTP) standard response code, in computer network communications, to indicate that the browser was able to communicate with a given server, but the server could not find what was requested. The error may also be used when a server does not wish to disclose whether it has the requested information."
The website hosting server will typically generate a "404 Not Found" web page when a user attempts to follow a broken or dead link; hence the 404 error is one of the most recognizable errors encountered on the World Wide Web. "
[End of quote]
So if you are looking for something you've previously found easily and frequently, some data link or control function somewhere has broken.
That makes total sense. Thank you for researching it Durdle and then sharing what you discovered. According to Just Asking it was due to some "bad" coding which was resolved and fixed. :)
Durdle 