I have a gridview which fetches its data from SQL server, The code that i have used is shown below using which i want to export the data into an excel sheet, but it throws the following exception 

Server Error in '/' Application.

---

Control 'ctl00_m_g_e5bb414f_98f1_49bc_a614_59a3719c12e4_ctl00_BlogGridView' of type 'GridView' must be placed inside a form tag with runat=server.

protected void ExportToExcel(object sender, EventArgs e)
        {
            Response.Clear();
            Response.Buffer = true;
            Response.AddHeader("content-disposition", "attachment;filename=GridViewExport.xls");
            Response.Charset = "";
            Response.ContentType = "application/vnd.ms-excel";
            using (StringWriter sw = new StringWriter())
            {
                HtmlTextWriter hw = new HtmlTextWriter(sw);

               
                BlogGridView.AllowPaging = false;
                this.gridview();

                BlogGridView.HeaderRow.BackColor = Color.White;
                foreach (TableCell cell in BlogGridView.HeaderRow.Cells)
                {
                    cell.BackColor = BlogGridView.HeaderStyle.BackColor;
                }
                foreach (GridViewRow row in BlogGridView.Rows)
                {
                    row.BackColor = Color.White;
                    foreach (TableCell cell in row.Cells)
                    {
                        if (row.RowIndex % 2 == 0)
                        {
                            cell.BackColor = BlogGridView.AlternatingRowStyle.BackColor;
                        }
                        else
                        {
                            cell.BackColor = BlogGridView.RowStyle.BackColor;
                        }
                        cell.CssClass = "textmode";
                    }
                }

BlogGridView.RenderControl(hw); <- Throws exception in this line

                //style to format numbers to string
                string style = @"<style> .textmode { mso-number-format:\@; } </style>";
                Response.Write(style);
                Response.Output.Write(sw.ToString());
                Response.Flush();
                Response.End();
            }
        }

what shall i do