ObjectDisposedException は処理されませんでした。プログラム終了時にセーフハンドルがクローズされた

class Program
{
    static void Main(string[] args)
    {
        System.Console.WriteLine("Begin: " + DateTime.Now.ToString());
        SystemCodeController sc = new SystemCodeController();
        sc.SyncSystemCodes();
        ParkingTicketController pt = new ParkingTicketController();
        pt.SyncParkingTickets();
        EmailHelper.SendSuccessEmail();
        System.Console.WriteLine("End: " + DateTime.Now.ToString());
    }
}

public void SyncParkingTickets()
{
    ptr.ClearTable();
    ptr.InsertNewCitation(ibmI.GetAllCitations());
    ptr.SaveChanges();
}

public void InsertNewCitation(IEnumerable<ParkingTicket> citations)
{
    foreach (ParkingTicket citation in citations)
    {
        InsertNewCitation(citation);
    }
}

public void InsertNewCitation(ParkingTicket citation)
{
    db.AddToParkingTickets(citation);
}

public IEnumerable<ParkingTicket> GetAllCitations()
{
    SystemCodeRepository scr = new SystemCodeRepository();

    //  Create SQL statement

    DataTable dt = new DataTable();
    using (iDB2Connection conn = new iDB2Connection(_connString))
    {
        using (iDB2Command cmd = new iDB2Command(sb.ToString(), conn))
        {
            conn.Open();
            using (iDB2DataAdapter da = new iDB2DataAdapter(cmd)) { da.Fill(dt); }
            conn.Close();
        }
    }

    #region Fill object from DataTable
    var citations = from i in dt.AsEnumerable()
                    select new ParkingTicket
                    {
                        // Fill object
                    };
    #endregion

    return citations;
}