RMAN DUPLICATE ON RAC DATABASE AND ORA-01503: CREATE CONTROLFILE failed

1. while performing RMAN Duplicate from a RAC database with active database, the operation fails with ora-12720 operation requires database is in EXCLUSIVE mode.

contents of Memory Script:
{
   sql clone "alter system set  db_name =
 ''RMANDP'' comment=
 ''Reset to original value by RMAN'' scope=spfile";
   sql clone "alter system reset  db_unique_name scope=spfile";
   shutdown clone immediate;
   startup clone nomount;
}
executing Memory Script

sql statement: alter system set  db_name =  ''RMANDP'' comment= ''Reset to original value by RMAN'' scope=spfile

sql statement: alter system reset  db_unique_name scope=spfile

Oracle instance shut down

connected to auxiliary database (not started)
Oracle instance started

Total System Global Area     275578880 bytes

Fixed Size                     2227584 bytes
Variable Size                159384192 bytes
Database Buffers             109051904 bytes
Redo Buffers                   4915200 bytes
sql statement: CREATE CONTROLFILE REUSE SET DATABASE "RMANDP" RESETLOGS ARCHIVELOG
  MAXLOGFILES    192
  MAXLOGMEMBERS      3
  MAXDATAFILES     1024
  MAXINSTANCES    32
  MAXLOGHISTORY      292
 LOGFILE
  GROUP   5  SIZE 100 M ,
  GROUP   6  SIZE 100 M
 DATAFILE
  '+DATA/rmandp/datafile/system.367.849426993'
 CHARACTER SET AL32UTF8

RMAN-00571: ===========================================================
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-00571: ===========================================================
RMAN-03002: failure of Duplicate Db command at 06/05/2014 08:03:41
RMAN-05501: aborting duplication of target database
RMAN-06136: ORACLE error from auxiliary database: ORA-01503: CREATE CONTROLFILE failed
ORA-12720: operation requires database is in EXCLUSIVE mode

2.Include the parameter cluster_database to false in the duplicate target statement as below to avoid the operation requires database is in exclusive mode error

RMAN> duplicate target database to rmandp
from active database
spfile
set db_name='rmandp'
set instance_number='1'
set control_files='+DATA','+DATA'
set cluster_database='false' # Avoid ORA-12720 error 
set log_file_name_convert='+DATA/orcl/','+DATA/rmandp/'
db_file_name_convert='+DATA/orcl/','+DATA/rmandp/';