Erreur php je ne comprend pas pourquoi !

<?php
$file ="txt.exe";
$url = "http://www.xxxxx.xx/test/txt.exe";
Header("Content-Disposition: attachment; filename=" . $file);
Header("Content-Type: application/force-download");
Header("Content-Transfer-Encoding: binary");
Header("Pragma: no-cache");
Header("Cache-Control: no-store, no-cache, must-revalidate, post-check=0, pre-check=0");
Header("Expires: 0");
readfile($url);
?>

<br />
<b>Warning</b>:  readfile(http://www.xxxxx.xx/test/txt.exe) [<a href='function.readfile'>function.readfile</a>]: failed to open stream: HHTTPrequest failed! HTTP/1.0 404 Not Found
 in <b>D:\production web\downloadfree.php</b> on line <b>10</b><br />