title: Excel generation, unreadable content
body: <p>I'm using <code>Apache POI 3.12</code> (<code>SXSSF</code> workbook) in order to generate <code>.xlsx</code> files. 
  The problem is that I'm doing the generation and when I open the file I'm receiving an error message:</p>
  
  <blockquote>
    <p>Excel found unreadable content in file.xlsx. Do you want to recover
    the contents of this workbook? If you trust the source of this
    workbook, click Yes.</p>
  </blockquote>
  
  <p>After clicking <code>Yes</code>, the file opens and I'm receiving this notification</p>
  
  <blockquote>
    <p>Excel completed file level validation and repair. Some parts of this
    workbook may have been repaired or discarded. Removed Records:
    Comments from /xl/comments1.xml part (Comments) Repaired Records:
    Comments from /xl/comments1.xml part (Comments)</p>
  </blockquote>
  
  <p>After that, I unzip the excel file and check the <code>comments1.xml</code>. All my comments are present. All 216 of them. </p>
  
  <p>The section of the code that generates the comments is the following</p>
  
  <pre><code>String comment = _propertiesHolder.getComment();
  String commentAuthor = _propertiesHolder.getCommentAuthor();
  if(comment != null)
  {
      int colIndex = cell.getColumnIndex();
      int rowIndex = cell.getRowIndex();
      CreationHelper helper = _workbook.getCreationHelper();
      ClientAnchor anchor = helper.createClientAnchor();
      anchor.setCol1(colIndex);
      anchor.setCol2(colIndex + 1);
      anchor.setRow1(rowIndex);
      anchor.setRow2(rowIndex + 3);
  
      // Create the comment and set the text+author
      Comment cellComment = _drawingPatriarch.createCellComment(anchor);
      if(commentAuthor != null)
      {
          cellComment.setAuthor(commentAuthor);
          RichTextString rs = helper.createRichTextString(commentAuthor + ": " + comment);
          cellComment.setString(rs);
      }
      else 
      {
          cellComment.setString(helper.createRichTextString(comment));
      }
  
      cellComment.setRow(rowIndex);
      cellComment.setColumn(colIndex);
  
      // Assign the comment to the cell
      cell.setCellComment(cellComment);
  }
  </code></pre>
  
  <p>Do you have any idea what could be the cause of this problem? Although no information was lost, clearly there is something wrong and I would like to fix it. The comments are retrieved from database (<code>varchar</code> datatype). The biggest comment is 138 characters long. </p>
  
  <p><strong>Update</strong></p>
  
  <p>Something that I forgot to mention. I've also run the same extraction using <code>hssf</code> implementation and no errors were present. It would be a safe assumption that the data are not the problem. </p>