当用户使用PHP Excel打开写入的xls文件时发出警告

The file you're trying to open [fileName] is in different format than specified by the file extension

I get that message whenever I open the xls files I've written using PHPExcel .. Is there anyway to get rid of that warning ,, the used code

<?php
require_once ('C:\wamp\www\phpexcel sample\Classes\PHPExcel\IOFactory.php');
$objPHPExcel = new PHPExcel();
$objPHPExcel->getProperties()->setCreator("7asobate")->setDescription("PHPExcel tryout");
$objPHPExcel->setActiveSheetIndex(0)->setTitle("7asobate worksheet")->setCellValue('A1' , 'someValue1')
->setCellValue('A2' , 'someValue2');
$objWriter = PHPExcel_IOFactory::createWriter($objPHPExcel , 'Excel2007');
$objWriter->save('F:\myFile.xls');
?>