RMAN flashback database to a restore point failed

Since my restore point is normal so I tried to flashback using rman and received RMAN-06004, ORA-01422.  I ran "select count(*) from dual;" and return only one row.  So it is not dual table problem.  Any suggestion?  William.
BANNER
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Oracle Database 10g Enterprise Edition Release 10.2.0.4.0 - 64bi
PL/SQL Release 10.2.0.4.0 - Production
CORE    10.2.0.4.0      Production
TNS for Linux: Version 10.2.0.4.0 - Production
NLSRTL Version 10.2.0.4.0 - Production
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rman target / catalog rman/password@catdb
Recovery Manager: Release 10.2.0.4.0 - Production on Wed Feb 24 18:33:40 2010

Copyright (c) 1982, 2007, Oracle.  All rights reserved.

connected to target database: TESTDB (DBID=3128547420, not open)
connected to recovery catalog database

RMAN> flashback database to restore point BEFORE_PATCH;