IE6下php header实现文件下载错误

if(strstr($_SERVER["HTTP_USER_AGENT"],"MSIE")==false) {
header("Cache-Control: no-cache");
header("Pragma: no-cache");
}

header('Cache-Control: public, must-revalidate, max-age=0');
header('Accept-Ranges: bytes');
header("Content-Type: application/force-download");
header("Content-Type: application/download");
header("Content-Type: application/octet-stream");
if(!empty($content_type)){
header("Content-Type: ".$content_type);
}
header("Content-Transfer-Encoding: binary");
header('Content-Disposition:attachment;filename="'.rawurlencode($filename).'"');