title: Error dialog displayed when opening an excel file generated with EPPlus
body: <p>I am creating an Excel file using the EPPlus library. When I create file and open up the file, the following pop up message shows:</p>
  
  <blockquote>
    <p>We found a problem with some content in 'ExcelDemo.xlsx'. Do you want us to try to recover as much as we can? If you trust the source of this workbook, Click Yes</p>
  </blockquote>
  
  <p>I am using following code </p>
  
  <pre><code>using (ExcelPackage pck = new ExcelPackage())
  {
      //Create the worksheet
      ExcelWorksheet ws = pck.Workbook.Worksheets.Add("Demo");
  
      //Load the datatable into the sheet, starting from cell A1. Print the column names on row 1
      ws.Cells[1, 2].Value = "Excel Download";
  
      Response.ContentType = "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet";
      Response.AddHeader("content-disposition", "attachment;  filename=ExcelDemo.xlsx");
      Response.BinaryWrite(pck.GetAsByteArray());
  }
  </code></pre>
  
  <p>Is there problem in my code or is this an Excel issue?</p>