令人沮丧的Sqlite3数据库被锁定错误

Question

我正在使用sqlite3进行ac＃.net4.5 win form application.i观察到，当我在表上使用UPDATE查询时遇到数据库被锁定错误另一方面SELECT查询在同一个表上没有给出任何错误。为什么会这样？

                //qryStrUQMFR = "SELECT * FROM loc_table_1 WHERE t_id =@t_id AND mem_id =@mem_id";
                qryStrUQMFR = "UPDATE loc_ loc_table_1 SET field1=@field1, field2=@field2, field3 =@field3, field4 =@field4 WHERE t_id =@t_id AND mem_id =@mem_id";

        try
        {
            using (SQLiteConnection conMRN = new SQLiteConnection(connectionString))
            {
                conMRN.Open();
                using (SQLiteTransaction tranMRN = conMRN.BeginTransaction())
                {
                    using (SQLiteCommand cmdMRN = new SQLiteCommand(qryStrUQMFR, conMRN))
                    {
                        cmdMRN.Parameters.Add("@t_id", DbType.Int32).Value = t_id;
                        cmdMRN.Parameters.Add("@mem_id", DbType.Int32).Value = mem_id;
            cmdMRN.Parameters.Add("@field1", DbType.Int32).Value = selAns;
                        cmdMRN.Parameters.Add("@field2", DbType.Int32).Value = qa;
                        cmdMRN.Parameters.Add("@field3", DbType.Int32).Value = qna;
                        cmdMRN.Parameters.Add("@field4", DbType.Int32).Value = qm;
                        cmdMRN.CommandType = CommandType.Text;
                        using (SQLiteDataReader rdrMRN = cmdMRN.ExecuteReader())
                        {
                            if (rdrMRN != null && rdrMRN.Read())
                            {
                //more code here                            
                            }
                        }// reader closed and disposed up here
                    }// command disposed here
                    tranMRN.Commit();
                }
            } //connection closed and disposed here
        }
        catch (SQLiteException ex)
        {
            MessageBox.Show("mrn-->" + ex.Message);
        }