Actually, the php functions are not case sensitive, but it's still a good idea to keep correct upper/lower case since everything else is.
Headers are terminated by CRLF, not LF, i.e. \r\n, although some agents replace \n by \r\n. So try conforming with standards and see if that helps.
Also, why the location header, and not just
require 'index.php';
This will save you an unnecessary request. a location redirect means the browser sends a new request to your server.