ORA-19573: cannot obtain exclusive enqueue for datafile during standby refresh from primary

Problem:
RMAN> RECOVER DATABASE NOREDO;

but I got an error:
RMAN-03002: failure of recover command at 12/01/2009 11:04:15
ORA-19870: error reading backup piece /oracle/rbackup.moon/ForStandby_2rkvqc1o_1_1
ORA-19573: cannot obtain exclusive enqueue for datafile 2

Description:
Unexpected ORA-XXX during refresh standby operation caused by 'RECOVER MANAGED STANDBY'


Solution:
SQLPLUS>ALTER DATABASE RECOVER MANAGED STANDBY DATABASE CANCEL;
RMAN> RECOVER DATABASE NOREDO;
enjoy...