title: Invalid file format when saving with PHPExcel
body: <pre><code>$file = '{full path and filename}';
  
  //Read file
  $file_type = PHPExcel_IOFactory::identify( $file );
  $excel_reader = PHPExcel_IOFactory::createReader($file_type);              
  $this-&gt;php_excel = $excel_reader-&gt;load($file);              
  
  //Set some values
  $this-&gt;php_excel-&gt;setActiveSheetIndex(0);
  $this-&gt;php_excel-&gt;getActiveSheet()-&gt;SetCellValue('A1', 'Hello');
  $this-&gt;php_excel-&gt;getActiveSheet()-&gt;SetCellValue('B2', 'world!');
  $this-&gt;php_excel-&gt;getActiveSheet()-&gt;SetCellValue('C1', 'Hello');
  $this-&gt;php_excel-&gt;getActiveSheet()-&gt;SetCellValue('D2', 'world!');
  
  //Write to file new location    
  $excel_writer = PHPExcel_IOFactory::createWriter($this-&gt;php_excel, 'Excel2007' );
  $excel_writer-&gt;save('c:\test.xls');
  </code></pre>
  
  <p>The <code>c:\test.xls</code> is created, but I get an error trying to load the Excel-file (from OpenOffice but I don't think that's the issue). The file I'm reading is about 260kb while the created test.xls is about 64kb. It says invalid and OpenOffice tries to repair the file when opening without success.</p>
  
  <p>What am I doing wrong?</p>