RMAN-05503: at least one auxiliary channel must be allocated to execute this command

RMAN-00571: ===========================================================
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-00571: ===========================================================
RMAN-03002: failure of Duplicate Db command at 06/05/2014 21:49:42
RMAN-05501: aborting duplication of target database
RMAN-05503: at least one auxiliary channel must be allocated to execute this command

Solution:-
allocate auxiliary channel plus regular channel for rman duplicate operation.

run
{
allocate  channel c1 device type disk connect 'sys/sys123@orcl1';
allocate  channel c2 device type disk connect 'sys/sys123@orcl2';
allocate  channel c3 device type disk connect 'sys/sys123@orcl1';
allocate auxiliary channel c4 device type disk ;
allocate auxiliary channel c5  device type disk ;
allocate auxiliary channel c6 device type disk;
duplicate target database to orcldp
spfile
parameter_value_convert='/u01/app/orcl/oracle/admin/orcl/adump','/u01/app/orcl/oracle/admin/orcldp/adump'
set dispatchers='(PROTOCOL=TCP) (SERVICE=orcldpXDB)'
set cluster_database='false'
set instance_number='1';
release channel c1;
release channel c2;
release channel c3;
release channel c4;
release channel c5;
release channel c6;
}