Error RMAN-20045: must specify FORMAT for BACKUP INCREMENTAL FROM SCN command

Error  "RMAN-20045"  during taking backup using RMAN
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RMAN> backup incremental from scn 1501331 database;

Starting backup at 11-SEP-17
using target database control file instead of recovery catalog
allocated channel: ORA_DISK_1
channel ORA_DISK_1: SID=54 device type=DISK
channel ORA_DISK_1: starting full datafile backup set
channel ORA_DISK_1: specifying datafile(s) in backup set
input datafile file number=00006 name=/u01/app/oracle/oradata/hr/test01.dbf
input datafile file number=00001 name=/u01/app/oracle/oradata/hr/system01.dbf
input datafile file number=00002 name=/u01/app/oracle/oradata/hr/sysaux01.dbf
input datafile file number=00005 name=/u01/app/oracle/oradata/hr/example01.dbf
input datafile file number=00003 name=/u01/app/oracle/oradata/hr/undotbs01.dbf
input datafile file number=00004 name=/u01/app/oracle/oradata/hr/users01.dbf
channel ORA_DISK_1: starting piece 1 at 11-SEP-17
RMAN-03009: failure of backup command on ORA_DISK_1 channel at 09/11/2017 09:09:16
RMAN-20045: must specify FORMAT for BACKUP INCREMENTAL FROM SCN command
continuing other job steps, job failed will not be re-run
channel ORA_DISK_1: starting full datafile backup set
channel ORA_DISK_1: specifying datafile(s) in backup set
including current control file in backup set
channel ORA_DISK_1: starting piece 1 at 11-SEP-17
RMAN-00571: ===========================================================
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-00571: ===========================================================
RMAN-03009: failure of backup command on ORA_DISK_1 channel at 09/11/2017 09:09:17
RMAN-20045: must specify FORMAT for BACKUP INCREMENTAL FROM SCN command


solution
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backup incremental from scn 1501331 database FORMAT '/u01/app/inc_backup/inc_bkp_%U';