Why is the .xls file not being read by means of the phpExcel library?

Question

phpspreadsheet

Code:
require_once('PHPExcel/IOFactory.php');
$xls = PHPExcel_IOFactory::load('xls.xls');
We open the page in the browser and see endless entries like this:
Notice: Uninitialized string offset: 1572863 in /home/bitrix/ext_www/path.to.site/xls/Classes/PHPExcel/Shared/OLERead.php on line 309
Notice: Uninitialized string offset: 1572860 in /home/bitrix/ext_www/path.to.site/xls/Classes/PHPExcel/Shared/OLERead.php on line 316
.......
What's wrong?