Oracle Distributed Transaction Error

using (System.Transactions.TransactionScope tx = 

    new System.Transactions.TransactionScope())

{

    //... Update data on SQL Server ...

    using (OracleConnection cn = new OracleConnection(cnStr))

    {

        cn.Open();

        OracleCommand cmdOra = new OracleCommand(

            "INSERT INTO MYLOG VALUES (SYSDATE, 'DEBUG')", cn);

        cmdOra.ExecuteNonQuery();

        cmdOra.CommandText = 

            "SELECT LOGTIME FROM MYLOG WHERE REMARK='DEBUG'";

        OracleDataReader dr = cmdOra.ExecuteReader();

        dr.Read();

        Response.Write(dr["LOGTIME"].ToString());

        dr.Close();

        cn.Close();

    }

    //tx.Complete();

    Response.Write("OK");

}