Filesperset cannot be used with copy

RMAN>  backup as copy
2> tag="db_bkp_incremental"
3> incremental level 0
4> duration 4:00 partial
5>  minimize time
6> filesperset 1
7> noexclude
8>  skip readonly
9> skip offline
10> skip inaccessible
11> database;

Starting backup at 17-may-2014 10:11:56
using channel ORA_DISK_1
using channel ORA_DISK_2
using channel ORA_DISK_3
using channel ORA_DISK_4
using channel ORA_DISK_5
RMAN-00571: ===========================================================
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-00571: ===========================================================
RMAN-03002: failure of backup command at 05/17/2014 10:11:58
RMAN-06580: the FPERSET option cannot be used with AS COPY

solution:

Remove filesperset from the backup as copy statement

RMAN> backup as copy
tag="db_bkp_incremental"
incremental level 0
duration 4:00 partial
 minimize time
noexclude
 skip readonly
skip offline
 skip inaccessible
 database;2> 3> 4> 5> 6> 7> 8> 9> 10>

Starting backup at 17-may-2014 10:14:50
using channel ORA_DISK_1
using channel ORA_DISK_2
using channel ORA_DISK_3
using channel ORA_DISK_4
using channel ORA_DISK_5
channel ORA_DISK_1: starting datafile copy
input datafile file number=00005 name=+DATA/cvrman/datafile/example.308.847525493