Exporting GridView to Excel - usual stuff isn't working

<asp:TemplateField HeaderText="Edit">
                    <ItemTemplate>
                        <asp:LinkButton runat="server" Text="Edit" CommandName="Edit" CausesValidation="false" />
                        <asp:LinkButton runat="server" Text="Delete" CommandName="Delete" CausesValidation="false" />
                    </ItemTemplate>
                    <EditItemTemplate>
                        <asp:LinkButton runat="server" Text="Update" CommandName="Update" CausesValidation="true" />
                        <asp:LinkButton runat="server" Text="Cancel" CommandName="Cancel" CausesValidation="false" />
                    </EditItemTemplate>
                    <FooterTemplate>
                        <asp:LinkButton ID="lnkAdd" runat="server" Text="Add" Width="80%" CommandName="Insert"
                            CausesValidation="true" ValidationGroup="OkToValidate" OnClick="lnkAdd_Click" />
                    </FooterTemplate>
                </asp:TemplateField>
///////////////////////////////////////////////////////
protected void btnExport_Click(object sender, ImageClickEventArgs e)
    {
        gvResult.AllowPaging = false;
        gvResult.ShowFooter = false;
        DataControlField dt;
        dt = gvResult.Columns[7];
        gvResult.Columns.Remove(gvResult.Columns[7]);
        Export("claimdir.xls", gvResult);
        gvResult.AllowPaging = true;
        gvResult.ShowFooter = true;
        gvResult.Columns.Insert(7, dt);
    }
 
    /// <summary>
    /// Got this online from http://mattberseth.com/
    /// </summary>
    /// <param name="fileName"></param>
    /// <param name="gv"></param>
    public static void Export(string fileName, GridView gv)
    {
        string style = @"<style> .mytext { mso-number-format:\@; } </style> ";
        HttpContext.Current.Response.Clear();
        HttpContext.Current.Response.AddHeader(
            "content-disposition", string.Format("attachment; filename={0}", fileName));
        HttpContext.Current.Response.ContentType = "application/ms-excel";
 
        using (StringWriter sw = new StringWriter())
        {
            using (HtmlTextWriter htw = new HtmlTextWriter(sw))
            {
                //  Create a table to contain the grid
                Table table = new Table();
 
                //  include the gridline settings
                table.GridLines = gv.GridLines;
 
                //  add the header row to the table
                if (gv.HeaderRow != null)
                {
                    PrepareControlForExport(gv.HeaderRow);
                    table.Rows.Add(gv.HeaderRow);
                }
 
                //  add each of the data rows to the table
                foreach (GridViewRow row in gv.Rows)
                {
                    PrepareControlForExport(row);
                    table.Rows.Add(row);
                }
 
                //  add the footer row to the table -- not in this page
                //if (gv.FooterRow != null)
                //{
                //    PrepareControlForExport(gv.FooterRow);
                //    table.Rows.Add(gv.FooterRow);
                //}
 
                //  render the table into the htmlwriter
                table.RenderControl(htw);
 
                //  render the htmlwriter into the response
                HttpContext.Current.Response.Write(style);
                HttpContext.Current.Response.Write(sw.ToString());
                HttpContext.Current.Response.End();
            }
        }
    }
 
    /// <summary>
    /// Replace any of the contained controls with literals
    /// Got this online from http://mattberseth.com/
    /// </summary>
    /// <param name="control"></param>
    private static void PrepareControlForExport(Control control)
    {
        for (int i = 0; i < control.Controls.Count; i++)
        {
            Control current = control.Controls[i];
            if (current is LinkButton)
            {
                control.Controls.Remove(current);
                control.Controls.AddAt(i, new LiteralControl((current as LinkButton).Text));
            }
            else if (current is ImageButton)
            {
                control.Controls.Remove(current);
                control.Controls.AddAt(i, new LiteralControl((current as ImageButton).AlternateText));
            }
            else if (current is HyperLink)
            {
                control.Controls.Remove(current);
                control.Controls.AddAt(i, new LiteralControl((current as HyperLink).Text));
            }
            else if (current is DropDownList)
            {
                control.Controls.Remove(current);
                control.Controls.AddAt(i, new LiteralControl((current as DropDownList).SelectedItem.Text));
            }
            else if (current is CheckBox)
            {
                control.Controls.Remove(current);
                control.Controls.AddAt(i, new LiteralControl((current as CheckBox).Checked ? "True" : "False"));
            }
            else if (current is TextBox)
            {
                control.Controls.Remove(current);
                control.Controls.AddAt(i, new LiteralControl((current as TextBox).Text));
            }
            else
            {
                control.Controls.Remove(current);
            }
 
            if (current.HasControls())
            {
                PrepareControlForExport(current);
            }
        }
    }