PHPExcel文件导出出现找不到该文件，高手

PHPExcel文件导出出现找不到该文件，求救高手！
环境：freeBSD服务器，PHP+MySQL
问题：做了一个excel导出功能，在windows本地与Linux测试环境都没有问题，在线上freeBSD出现找不到该文件。

PHP code

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        $file_name = isset($_GET['exam_caption']) && !empty($_GET['exam_caption']) ?   $_GET['exam_caption'] : time().mt_rand(1000, 9999);
        $outputFileName = iconv ( 'UTF-8', 'gb2312', $file_name . '.xlsx' );
        header ( 'Pragma:public' );
        header ( 'Expires:0' );
        header ( 'Cache-Control:must-revalidate,post-check=0,pre-check=0' );
        header ( 'Content-Type:application/force-download' );
        header ( 'Content-Type:application/vnd.ms-excel' );
        header ( 'Content-Type:application/octet-stream' );
        header ( 'Content-Type:application/download' );
        header ( 'Content-Disposition:attachment;filename=' . $outputFileName );
        header ( 'Content-Transfer-Encoding:binary' );
        $objWriter->save ( 'php://output' );

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