gautier on "send_headers on IE"

Do someone know why this code isn't woring on IE?

add_action('send_headers','site_router');
function site_router(){
$url = str_replace($root ,'',$_SERVER['REQUEST_URI']);
$url = explode('/',$url);
if(count($url) == 1 && $url[0] == 'portfolio'){
require 'tpl-portfolio.php';
die();
}
}