PHP Script Error

Im trying to write a PHP script that will allow the downloading of Windows Media Video files (.wmv) I came up with this:

header('Content-Description: File Transfer');
header("Content-type: application/force-download");  
header("Content-type: video/x-ms-wmv");
header('Content-Disposition: attachment; filename='.basename($file));
header('Content-Transfer-Encoding: binary');
header('Expires: 0');
header('Cache-Control: must-revalidate, post-check=0, pre-check=0');
header('Pragma: public');
header('Content-Length: ' . filesize($file));
ob_clean();
flush();
readfile($Dfile);

The problem is that it will bring up a save as dialog box for anything else but .wmv files. I was ale to download a .mp3 and .jpg etc... but for some reason .wmv will not come up it just dies. Can anyone help me with this, maybe tell me what Im missing?