my dynamic ddl selectindexchanged is not firing

public void LoadControlData(System.Web.UI.WebControls.Table t, bool IsPostBack, params object[] parameters)
        {
            DataTable dt1 = new DataTable();
            DataTable dt2 = new DataTable();
            IReportData reportInputData = new FieldAuditActivityForDistrictsReportData();
            DataSet ds = reportInputData.GetReportInputData();

            if (IsPostBack == true)
            {
                DropDownList ddlTaxType = (DropDownList)t.FindControl("ddlRegionID");
                ddlTaxType.AppendDataBoundItems = true;
                ddlTaxType.Items.Insert(0, "");
                ddlTaxType.SelectedIndex = 0;
                ddlTaxType.DataSource = ds.Tables[0];
                ddlTaxType.DataTextField = "RegionName";
                ddlTaxType.DataValueField = "RegionID";
                _regionID =ddlTaxType.DataValueField;
                ddlTaxType.DataBind();

                //DropDownList ddlAuditors = (DropDownList)t.FindControl("ddlOfficeID");
                //ddlAuditors.AppendDataBoundItems = true;
                //ddlAuditors.Items.Insert(0, "");
                //ddlAuditors.SelectedIndex = 0;
                //ddlAuditors.DataSource = ds.Tables[1];
                //ddlAuditors.DataTextField = "OfficeName";
                //ddlAuditors.DataValueField = "OfficeID";
                //ddlAuditors.DataBind();
            }

            _tableHold = t;

            _lbuttoned = (LinkButton)t.FindControl("lbuttonEndDateID");
            _ddlRegion = (DropDownList)t.FindControl("ddlRegionID");
            Calendar cldred = (Calendar)t.FindControl("cldrEndDateID");
            _lbuttoned.Click += new EventHandler(lbuttoned_Click);   
            cldred.SelectionChanged += new EventHandler(cldred_SelectionChanged);
            cldred.VisibleMonthChanged += new MonthChangedEventHandler(cldred_VisibleMonthChanged);
            cldred.Visible = false;
            _ddlRegion.SelectedIndexChanged += new EventHandler(ddlRegion_SelectedIndexChanged);
            //_ddlRegion.SelectedIndexChanged += new EventHandler(ddlRegion_SelectedIndexChanged);
        }



public void ddlRegion_SelectedIndexChanged(object sender, EventArgs e)
        {
            DataRow dr = null;            
            IDataAccess da = DataAccessFactory.Create("ATS");
            List<idbdataparameter> pars = new List<idbdataparameter>();
            IDbDataParameter param1 = new SqlParameter(DataConstants.DataConstants.REGION_ID,_regionID);
            pars.Add(param1);

            SqlDataReader reader = (SqlDataReader)da.ExecuteReader(ProcedureConstants.FIELD_AUDIT_ACTIVITY_FOR_DISTRICTS_DISTRICTS_INPUT, ref pars, true);

            DataTable dt = new DataTable();

            DataColumn dc1 = new DataColumn("officeid");
            DataColumn dc2 = new DataColumn("officename");


            dt.Columns.Add(dc1);
            dt.Columns.Add(dc2);

            while (reader.Read())
            {
                dr = dt.NewRow();
                dr[dc1] = reader["officeid"];
                dr[dc2] = reader["officename"];
                dt.Rows.Add(dr);
            }

            DataSet ds = new DataSet();
            ds.Tables.Add(dt);
            
            //DropDownList ddlTaxType = (DropDownList)t.FindControl("ddlRegionID");
            //ddlTaxType.AppendDataBoundItems = true;
            //ddlTaxType.Items.Insert(0, "");
            //ddlTaxType.SelectedIndex = 0;
            //ddlTaxType.DataSource = ds.Tables[0];
            //ddlTaxType.DataTextField = "RegionName";
            //ddlTaxType.DataValueField = "RegionID";
            //_regionID = ddlTaxType.DataValueField;
            //ddlTaxType.DataBind();
        }