gridview data is not exporting to excel.

protected void btnExport_Click(object sender, EventArgs e)
    {
        if (lblMsg.Visible == true)
        {
            Response.Redirect("~/Reports.aspx");
        }


        Response.ClearContent();
        Response.AppendHeader("content-disposition", "attachment;filename=FirstExport.xls");
        Response.ContentType = "application/excel";
        StringWriter stringWriter = new StringWriter();
        HtmlTextWriter htmlTextWriter = new HtmlTextWriter(stringWriter);

        gridName.AllowPaging = false;
        gridName.DataBind();

        gridName.HeaderRow.Style.Add("background-color", "#FFFFFF");
        foreach (TableCell tableCell in gridName.HeaderRow.Cells)
        {
            tableCell.Style["background-color"] = "#A55129";
        }
        foreach (GridViewRow gridViewRow in gridName.Rows)
        {
            gridViewRow.BackColor = System.Drawing.Color.White;
            foreach (TableCell gridViewRowTableCell in gridViewRow.Cells)
            {
                gridViewRowTableCell.Style["background-color"] = "#FFF7E7";
            }
        }

        gridName.RenderControl(htmlTextWriter);
        Response.Write(stringWriter.ToString());
        Response.End();
        gridName.AllowPaging = true;
    }