Grid view not displaying when Text file Generating After Grid View Bind

public void gridviewfill()
{
ds = ObjOrdersBll.Invoice_Status_Report(ObjOrdersBo);

if (ds.Tables[0].Rows.Count > 0)
{
   if (txtInvoiceNo.Text == "")
   {
       for (int i = 0; i < ds.Tables[0].Rows.Count; i++)
       {
           //ds.Tables[0].Rows[i]["DeliveryDate"] = Convert.ToDateTime(ds.Tables[0].Rows[i].ItemArray[1]).ToString("yyyyMMdd");
           //ds.Tables[0].Rows[i]["DeliveryTime"] = ds.Tables[0].Rows[i].ItemArray[2].ToString();//.Replace(':',' ').ToString();
           ds.Tables[0].Rows[i]["FromDate"] = DateText(ds.Tables[0].Rows[i].ItemArray[4].ToString());
           ds.Tables[0].Rows[i]["Todate"] = DateText(ds.Tables[0].Rows[i].ItemArray[5].ToString());
       }
   }

   dtExport = ds.Tables[0];


   gdvInvoices.DataSource = ds.Tables[0];
   gdvInvoices.DataBind();
   gdvInvoices.Enabled = true;
   gdvInvoices.Visible = true;

   //DataTableToTextFile(dtExport, Server.MapPath("TempImages\\Invoice_Report.txt"));
   BindText(Server.MapPath("TempImages\\Invoice_Report.txt"));

   Clear();
}

public void BindText(string filePath)
{
    try
    {
        string attachFileName = "Invoice" + DateTime.Now.ToString("yyyyMMddHHmmss") + ".txt";  
        System.IO.FileInfo file = new System.IO.FileInfo(filePath);
        Response.ClearContent();
        Response.AddHeader("content-disposition", "attachment; filename=" + attachFileName);
        StringBuilder str = new StringBuilder();
        for (int i = 0; i < gdvInvoices.Columns.Count; i++)
        {
            str.Append(gdvInvoices.Columns[i].HeaderText + ',');
        }
        str.Append("\n");
        for (int j = 0; j < gdvInvoices.Rows.Count; j++)
        {
            for (int k = 0; k < gdvInvoices.Columns.Count; k++)
            {
                str.Append(gdvInvoices.Rows[j].Cells[k].Text + ',');
            }
            str.Append("\n");
        }
        Response.Write(str.ToString());
       
        Response.End();

        System.Threading.Thread.Sleep(3000);
        Clear();
    }
    catch (Exception ex) { }
}