title: PHPExcel file cannot open because the file format or file extension is not valid
body: <p>I  developed wordpress plugin to export custom post content to excel file using PHPExcel library and everything works fine at my local machine when I uploaded the plugin to the server this error appears when I open the excel file</p>
  
  <pre><code>file cannot open file because the file format or file extension is not valid
  </code></pre>
  
  <p>I opened the excel file in notepad to see what is the error, I found this</p>
  
  <pre><code>Parse error: syntax error, unexpected '[', expecting ')' in /Classes/PHPExcel/Writer/Excel2007/Chart.php on line 637
  </code></pre>
  
  <p>php version running on the server 5.3.28-1</p>
  
  <p>how can I fix this</p>
  
  <p>thank you</p>