SQL & PL/SQL

Hi all,

I made a table like below,
==============================
CREATE TABLE ser_1m_det (
time TIMESTAMP,
proto NUMBER(3,0),
port NUMBER(5,0),
pkts NUMBER(17,0),
vol_m NUMBER(17,4)
);
====================================

Then I want to use below SQL
====================================
SELECT proto, port, SUM(pkts) pkts, SUM(vol_m) vol_m
FROM ser_1m_det
GROUP BY (proto, port)
HAVING time < SYSTIMESTAMP AND ROWNUM<10
ORDER BY SUM(pkts);
====================================

When I execute upper sql, I met this error message;
===================================
ORDER BY SUM(pkts)
*
ORA-00935 group function is nested too deeply
===================================

Then I search what this message mean.
====================================
ORA-00935 group function is nested too deeply

Cause: This is an internal error message not usually issued.

Action: Contact Oracle Support Services.
====================================

I install Oracle9iAS Infrastructure 9.0.2.0.0 on WIN2000.
(I am using DBMS in Oracle9iAS @.@)
-> DBMS version is Oracle9i Enterprise Edition Release 9.0.1.3.1
Anybody know why I met upper error message?

Thanks in advance.