Oracle Database Discussions

Hi,
on 10g R2, why I can not use Flash version query even if I use a large time interval :

SQL> SELECT versions_startscn, versions_starttime,
  2         versions_endscn, versions_endtime,
  3         versions_xid, versions_operation,
  4  ename from  scott.EMP
  5  VERSIONS BETWEEN TIMESTAMP
  6        TO_TIMESTAMP('2003-07-18 14:00:00', 'YYYY-MM-DD HH24:MI:SS')
  7    AND TO_TIMESTAMP('2010-07-18 17:00:00', 'YYYY-MM-DD HH24:MI:SS')
  8  ;
ename from  scott.EMP
                  *
ERROR at line 4:
ORA-08180: no snapshot found based on specified time


SQL> select ename, sal from scott.emp;

ENAME             SAL
---------- ----------
SMITH             800

SQL> update scott.emp set SAL=SAL*2 where ename='SMITH';

1 row updated.

SQL> select ename, sal from scott.emp;

ENAME             SAL
---------- ----------
SMITH            1600

SQL> SELECT versions_startscn, versions_starttime, 
       versions_endscn, versions_endtime,
       versions_xid, versions_operation,
ename from  scott.EMP
VERSIONS BETWEEN TIMESTAMP 
      TO_TIMESTAMP('2003-07-18 14:00:00', 'YYYY-MM-DD HH24:MI:SS')
  AND TO_TIMESTAMP('2010-07-18 17:00:00', 'YYYY-MM-DD HH24:MI:SS')
ename from  scott.EMP
                  *
ERROR at line 4:
ORA-08180: no snapshot found based on specified time


SQL> commit;

Commit complete.

SQL> SELECT versions_startscn, versions_starttime,
  2         versions_endscn, versions_endtime,
  3         versions_xid, versions_operation,
  4  ename from  scott.EMP
  5  VERSIONS BETWEEN TIMESTAMP
  6        TO_TIMESTAMP('2003-07-18 14:00:00', 'YYYY-MM-DD HH24:MI:SS')
  7    AND TO_TIMESTAMP('2010-07-18 17:00:00', 'YYYY-MM-DD HH24:MI:SS')
  8  ;
ename from  scott.EMP
                  *
ERROR at line 4:
ORA-08180: no snapshot found based on specified time

Thank you.
PS :

ORA-08180: no snapshot found based on specified time 
Cause: Could not match the time to an SCN from the mapping table.
 
Action: try using a larger time.