How to set Dunstan Error page for 404 Page not found?

In order to activate the Dunstan-style Error Page plugin, I needed the API code.

How to get API code – wordpress?

There in Settings >>> Error Page >>> Enter the API code

Now my Dunstan-style Error Page is working.

But somehow its working only for 3 blogs!

Why on earth its not working for the 4th blog .

Ok I Found the culprit!!!!!!!!

Dunstan Error 404 works only with Permalinks setting  with “Index” i.e.    /index.php/%year%/%postname%/

No other permalinks setting will work for Dunstan 404 error page!