NpgsqlConnection conn = new NpgsqlConnection(MainForm2.MyConString);
        {
            conn.Open();
            using (NpgsqlCommand cmd = new NpgsqlCommand("SELECT rfid,name,sc_id from passenger ORDER by name",conn))
            {
                NpgsqlDataReader dr = cmd.ExecuteReader();
                while (dr.Read())
                {
                    var obj = new PassengerClass
                    {
                        RFID = dr.GetString(0),Name = dr.GetString(1),sc_id = dr.GetInt32(2)
                    };
                    s = dr.GetString(0);
                    try { ret.Add(s,obj); }
                    catch (Exception ex) { SM.Debug("Fail to add RFID Name in hash RFID:" + s + ex.ToString()); }
                }
            }
            MainForm2.PassHash = ret;
            try
            {
                using (NpgsqlCommand cmd = new NpgsqlCommand(string.Format("UPDATE place set useridx ={0} where useridx=0",MainForm2.userIDX),conn))
                    cmd.ExecuteNonQuery();

                using (NpgsqlCommand cmd = new NpgsqlCommand(string.Format("UPDATE zonename set useridx ={0} where useridx=0",conn))
                    cmd.ExecuteNonQuery();
            }
            catch (Exception ex)
            {
                SM.Debug("Error on update users IDX for place and zone with value 0 :" + ex.ToString());
            }

所以,在第二个命令语句中,它给出了以下错误：

A first chance exception of type ‘System.InvalidOperationException’
occurred in Npgsql.dll

Additional information: An operation is already in progress.

编辑附加信息：