title: Opening excel files from the internet opens a blank excel window
body: <p>A method in dumping a GridView to an Excel file to download/open from the internet was recently broken with new Windows Updates.</p>
  
  <p>My code dumps from a GridView to an XLS file using StringWriter, HTMLTextWriter and RenderControl. A common approach using the following code from <a href="http://www.aspsnippets.com/Articles/Export-GridView-to-Excel-in-ASPNet-with-Formatting-using-C-and-VBNet.aspx" rel="noreferrer">http://www.aspsnippets.com/Articles/Export-GridView-to-Excel-in-ASPNet-with-Formatting-using-C-and-VBNet.aspx</a></p>
  
  <pre><code>Protected Sub ExportToExcel(sender As Object, e As EventArgs)
      Response.Clear()
      Response.Buffer = True
      Response.AddHeader("content-disposition", "attachment;filename=GridViewExport.xls")
      Response.Charset = ""
      Response.ContentType = "application/vnd.ms-excel"
      Using sw As New StringWriter()
          Dim hw As New HtmlTextWriter(sw)
  
          'To Export all pages
          GridView1.AllowPaging = False
          Me.BindGrid()
  
          GridView1.HeaderRow.BackColor = Color.White
          For Each cell As TableCell In GridView1.HeaderRow.Cells
              cell.BackColor = GridView1.HeaderStyle.BackColor
          Next
          For Each row As GridViewRow In GridView1.Rows
              row.BackColor = Color.White
              For Each cell As TableCell In row.Cells
                  If row.RowIndex Mod 2 = 0 Then
                      cell.BackColor = GridView1.AlternatingRowStyle.BackColor
                  Else
                      cell.BackColor = GridView1.RowStyle.BackColor
                  End If
                  cell.CssClass = "textmode"
              Next
          Next
  
          GridView1.RenderControl(hw)
          'style to format numbers to string
          Dim style As String = "&lt;style&gt; .textmode { } &lt;/style&gt;"
          Response.Write(style)
          Response.Output.Write(sw.ToString())
          Response.Flush()
          Response.[End]()
      End Using
  End Sub
  
  Public Overrides Sub VerifyRenderingInServerForm(control As Control)
      ' Verifies that the control is rendered
  End Sub
  </code></pre>
  
  <p>Excel (2013) will open to a blank window, with no warning or message as to why anything was blocked, and without option to accept the file to open.</p>
  
  <p>My code is run on an intranet site, and I do have access to group policies / settings / user configurations in Windows.</p>