Excel Export attachments not displaying

public void Export(string fileName, GridView gv) 
        { 
            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 form to contain the grid  
                    Table table = new Table(); 
                     
                    table.GridLines = GridLines.Both; 
                     
 
                    //  add the header row to the table  
                    if (gv.HeaderRow != null) 
                    { 
                        PrepareControlForExport(gv.HeaderRow); 
                        table.Rows.Add(getheader()); 
                        table.Rows.Add(gv.HeaderRow); 
                        table.Rows[0].BackColor = System.Drawing.Color.FromArgb(37, 96, 133); 
                    } 
 
                    //  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  
                    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(sw.ToString()); 
                    HttpContext.Current.Response.End(); 
                } 
            } 
        } 
 
 
/// <summary>  
        /// Replace any of the contained controls with literals  
        /// </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")); 
                } 
 
                if (current.HasControls()) 
                { 
                    PrepareControlForExport(current); 
                } 
            } 
        }