ORA-19573: cannot obtain exclusive enqueue for datafile

Starting restore at 01-MAY-13
using target database control file instead of recovery catalog
allocated channel: ORA_DISK_1
channel ORA_DISK_1: sid=141 devtype=DISK
channel ORA_DISK_1: starting datafile backupset restore
channel ORA_DISK_1: specifying datafile(s) to restore from backup set
restoring datafile 00004 to /home/oracle/10.2.0/product/oradata/MYDB/users01.dbf
channel ORA_DISK_1: reading from backup piece /home/oracle/10.2.0/product/flash_recovery_area/MYDB/backupset/2013_05_01/o1_mf_nnndf_TAG20130501T123051_8r1hf39t_.bkp
RMAN-00571: ===========================================================
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-00571: ===========================================================
RMAN-03002: failure of restore command at 05/01/2013 12:45:20
ORA-19870: error reading backup piece /home/oracle/10.2.0/product/flash_recovery_area/MYDB/backupset/2013_05_01/o1_mf_nnndf_TAG20130501T123051_8r1hf39t_.bkp
ORA-19573: cannot obtain exclusive enqueue for datafile 4

Cause

Restore opration is try to overwrite the currently active version of the datafile .i.e Restore command  have been fired  for datafile which is currntly restoring  from other sesstion or datafile is online which you are restoring .

Solution

1) Bring the datafile offline
2) Restart database in mount state
3) Cancle the duplicate session if you start restore on same file at same time