ORA-19573: cannot obtain exclusive enqueue for datafile 8

$ ./rman target / nocatalog

Recovery Manager: Release 10.2.0.4.0 - Production on Sun Oct 06 13:55:43 2013

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connected to target database: SSAERP (DBID=3389811866, not open)
using target database control file instead of recovery catalog

RMAN>  RECOVER DATABASE NOREDO;

Starting recover at 06-Oct-13
allocated channel: ORA_SBT_TAPE_1
channel ORA_SBT_TAPE_1: sid=1982 devtype=SBT_TAPE
channel ORA_SBT_TAPE_1: Veritas NetBackup for Oracle - Release 6.5 (2007072323)
allocated channel: ORA_DISK_1
channel ORA_DISK_1: sid=982 devtype=DISK
channel ORA_DISK_1: starting incremental datafile backupset restore
channel ORA_DISK_1: specifying datafile(s) to restore from backup set
destination for restore of datafile 00008: /ora_dat/drssaerp/xdb_SSAERP02.dbf
destination for restore of datafile 00019: /ora_idx/drssaerp/idb_SSAERP02.dbf
channel ORA_DISK_1: reading from backup piece /ora_idx/drssaerp/bk/forstandby_l ptes4o_1_1
RMAN-00571: ===========================================================
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-00571: ===========================================================
RMAN-03002: failure of recover command at 06/10/2013 13:57:11
ORA-19870: error reading backup piece /ora_idx/drssaerp/bk/forstandby_lvptes4o_1 _1
ORA-19573: cannot obtain exclusive enqueue for datafile 8


Solution:

It seems database is open mode for which performing restore
Shutdown database and put the mount stage and start recovery.