Delete ข้อมูลใน Gridview ในแต่ละ Row เเต่ขึ้น Error

  protected void GridView8_RowDeleting(object sender, GridViewDeleteEventArgs e)
             {
                 string fileid = GridViewTool.getCellText((GridView)sender, e.RowIndex, "FILEID");
                 string datetime = GridViewTool.getCellText((GridView)sender, e.RowIndex, "DATETIME");

                 IDBHandler _THDBConn = null;
                 try
                 {
                     //_THDBConn = DBHandleBuilder.GetConnection(Constant.DB_NID, _logger);
                     _THDBConn = DBHandleBuilder.GetConnection(Constant.DB_BOONG, _logger);

                     FileDamage_DAO orderDao = new FileDamage_DAO(_logger);
                     orderDao.GetDelete(_THDBConn, fileid,datetime);
                     //showStartUpMessage("ShowDelete", "OrderNo" + orderNo + " is Delete data Success.");
                     SetgvBarcode(_THDBConn);  
                 }
                 catch (Exception ex)
                 {
                     showStartUpMessage("RemoveErpOrderInfo", "Error happened:" + ex.ToString());
                 }
                 finally
                 {
                     if (_THDBConn != null)
                     {
                         _THDBConn.Dispose();
                     }
                 }
                 //GridView8.DataSource = dt;
                 //GridView8.DataBind();
                 //ShowDataAl();
                 
             }
             private void SetgvBarcode(IDBHandler conn)
             {
                 FileDamage_DAO dao = new FileDamage_DAO(_logger);
                 //List<ErpOrderInfoVO> erpOrderList = dao.queryErpOrderList(conn, "%" + txtOrderNo.Text + "%", ddlProductID.SelectedValue, true);

                 DataTable dt = new DataTable();
                 dt.Columns.Add("FILEID");
                 //dt.Columns.Add("DATETIME");
   

                 this.GridView8.DataSource = null;
                 this.GridView8.DataBind();

             }
             private void showStartUpMessage(string key, string msg)
             {
                 string scriptMsg = msg.Replace("\\", "\\\\").Replace("'", "\\'").Replace("\r", "").Replace("\n", "\\n");
                 Page.ClientScript.RegisterStartupScript(Page.GetType(), key, "alert('" + scriptMsg + "');", true);
             }

 public int GetDelete(IDBHandler conn, string fileid, string datetime)
      {
          //DataTable dtTmp = new DataTable();
          //StringBuilder sb = null;
          _logger.Info(" deleteBarcodeInfo() - Start ");
          try
          {
              //sb = new StringBuilder();

              string sql = " DELETE FROM VDATA D, VCTRL C  "
                         + " WHERE C.fileid = '" + fileid + "'" 
                         + " AND D.vctrlid = C.vctrlid  "
                         + " AND datetime = TO_DATE('" + datetime + "', 'MM/DD/YYYY HH24:MI:SS') ";

              int deleteCnt = conn.ExecuteNonQuery(sql, false);
              _logger.Info(" deleteBarcodeInfo() - End ");
              return deleteCnt;
          }
          catch (Exception ex)
          {
              _logger.Info(ex);
              throw ex;
          }
}