Custom 404 error messages in IIS

To set up a custom 404 error message on Windows in IIS, there are the following things to keep in mind when using PHP files:

1. The custom 404 file cannot be a server-side executable script like PHP or ASP, it has to be a flat HTML file (.htm or .html extension is fine).

2. The .PHP extension handling has to have the checkbox "verify that the file exists" checked in order to see the custom 404 error page if a .php extension is used in the URL.

3. Restarting the website after setting these changes might help.