private void Save()
        {
            // save to database
            DB.Open();
            DB.BeginTransaction();
            try
            {
                ChecklistRulesAddNew checklistRulesAddNew = new ChecklistRulesAddNew(checklistRulesAddTDS);
                checklistRulesAddNew.Save(arrayCategoriesSelected, arrayCompanyLevelsSelected, arrayUnitsSelected);

                // Store datasets
                checklistRulesAddTDS.AcceptChanges();
                Session["checklistRulesAddTDS"] = checklistRulesAddTDS;

                DB.CommitTransaction();
            }
            catch (Exception ex)
            {
                DB.RollbackTransaction();

                string url = string.Format("./../../error_page.aspx?error={0}", ex.Message.Replace('\n', ' '));
                Response.Redirect(url);
            }
        }