What is the cause if a Page cannot be found message is display when opening a web page other than your homepage?

What is the cause if a Page cannot be found message is display when opening a web page other than your homepage?

Most likely causes are
A: you \ or a co-worker moved the page (if we are talking about a website you own)
B: you\or a co-worker deleted the page
C: the link was misspelled

If you are talking about regular websites and not a site you own the above still applies just take out the "you\ or a coworker". I see the A and B examples on the web much, much more than the C example.

add to the above, miss-spelled includes case-sensitive servers where this.jpg may not be the same as this.JPG