actionscript 3 - Flash无法识别AS3 PHP的文件类型

我在as3flash和php编程一个按钮，你可以下载文件。zip文件。它从php(代理)获取路径，但它不能识别文件类型，也不能运行COMPLETE事件。这样做的目的是隐藏zip文件所在的位置。我不明白问题出在哪里。as3代码:

package {
    imports...
    public class Main extends MovieClip{
        var download_button:MovieClip;
        var req:URLRequest;
        var file:FileReference;
        var proxy:String = "http://www.domain.com/audio/proxy.php?url=";
        var filename:String = "file.zip";
        var status:TextField = new TextField();
        public function Main() {
            download_btn.addEventListener(MouseEvent.CLICK, promptDownload);
            status.text = "Bienvenido";
            addChild(status);
        }
        private function promptDownload(e:MouseEvent):void {
            req = new URLRequest(proxy + filename);
            file = new FileReference();
            file.addEventListener(Event.COMPLETE, completeHandler);
            file.addEventListener(Event.CANCEL, cancelHandler);
            file.addEventListener(IOErrorEvent.IO_ERROR, ioErrorHandler);
            file.download(req, "file.zip");
        }
        private function cancelHandler(event:Event):void {
            trace("User canceled the download");
            status.text = "Cancelado";
        }
        private function completeHandler(event:Event):void {
            trace("Download complete");
            status.text = "Completado";
        }
        private function ioErrorHandler(event:IOErrorEvent):void {
            trace("ioError occurred");
            status.text = "Error";
        }
    }
}

和PHP代码:

$filename = "http://www.domain.com/audio/files" . $_GET['url'];
$archivo = "file.zip";
$len = filesize($filename);
$outname = $archivo;
header("Content-type: application/zip");
// Optional but the error is the same
//header("Expires: -1");
//header("Last-Modified: " . gmdate('D, d M Y H:i:s') . " GMT");
//header("Content-Transfer-Encoding: binary");
//header("Cache-Control: no-store, no-cache, must-revalidate");
//header("Cache-Control: post-check=0, pre-check=0");
//header("Pragma: no-cache");
//header("Content-Length:".$len);
//header("Content-Disposition: attachment; filename=".$outname);
readfile($filename);

非常感谢