Opening excel files from the internet opens a blank excel window
<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>