ทำไฟล์ popup download แล้วติด Warning: Cannot modify header information ช่วยหน่อยคับ แก้หลายวันแร้ว

<?php
$path	=	'attach';
$filename = $path.'/'.$_GET['file'];
$filename = realpath($filename);

ob_start();
header("Pragma: public");
header("Expires: 0");
header("Cache-Control: must-revalidate, post-check=0, pre-check=0");
header("Cache-Control: public");
header("Content-Description: File Transfer");
header('Content-Type: application/octet-stream');
header("Content-Disposition: attachment; filename=\"{$filename}\"");
header("Content-Transfer-Encoding: binary");
ob_end_flush();
readfile($filename);
?>