phpexcel can't get not empty value - php

Question

I use phpexcel to read a table,but sometimes it can't get value which is not empty.
import('ORG.PHPExcel');
import('ORG.PHPExcel.IOFactory');
import('ORG.PHPExcel.Reader.Excel5');
import('PHPExcel.Reader.Excel2007');
$objReader = new PHPExcel_Reader_Excel5();
$objReader->setReadDataOnly(true);
//use excel2007
$objPHPExcel = new PHPExcel();
$objPHPExcel = $objReader->load($uploadfile);
$sheet = $objPHPExcel->getSheet(1);
$highestRow = $sheet->getHighestRow();
var_dump($highestRow);
$highestColumn = $sheet->getHighestColumn();
var_dump($highestColumn);
$count=0;
$zzdw = M('zzdw');
for($j=4;$j<=$highestRow;$j++)
{
$count++;
$flag=0;
$b= (string)$objPHPExcel->getActiveSheet()->getCell("B".$j)->getValue();
if($b==''){
echo('<font color="red"><strong>'.$count.'</strong></font>');
var_dump($b);
exit;
}
}
result
like this, row and col have value,but can't get cell's value.
some files don't have this problem,some have.
file format error？I use ".xls".