UNIX-servers are case-sensitive - they distinguish between upper-case and lowercase letters in file names and folder names. So if you move your website from a windows to a UNIX-server (when you change web host for instance), you risk getting a certain amount of "Page not found"-errors (404 errors), because directories and other websites linking to yours sometimes get the cases wrong (typically writing the first letter of folder names in upper-case etc.).
This javascript-based custom 404-error page solves the problem by converting URL's into lowercase.
