Readie - 8:46 pm on May 31, 2013 (gmt 0)
In the past when looking up the 404 header (I can't remember the syntax for everything :) ) I've seen people advise the following:
header('HTTP/1.0 404 Not Found', true, 404);
header('Status: 404 Not Found');
I'm not sure if having them both really makes any difference though.