ORA-19806: cannot make duplex backups in recovery area

when running "backup filesperset 10 archivelog all not backed up 2 times;", encountered below error :

channel ORA_DISK_1: starting piece 1 at 2016-MAY-25 14:59:18
RMAN-00571: ===========================================================
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-00571: ===========================================================
RMAN-03009: failure of backup command on ORA_DISK_1 channel at 05/25/2016 14:59:18
ORA-19806: cannot make duplex backups in recovery area

Initially thought FRA is full, but it is not.

SYS@PELD> @@chk_fra_usage

NAME

------------------------------------------------------------------------------------------------------------------------------------

SPACE_LIMIT SPACE_USED SPACE_RECLAIMABLE NUMBER_OF_FILES

----------- ---------- ----------------- ---------------

/dbfra/testdb01d

 5.3687E+10  959854592                 0              20

FILE_TYPE            PERCENT_SPACE_USED PERCENT_SPACE_RECLAIMABLE NUMBER_OF_FILES

-------------------- ------------------ ------------------------- ---------------

CONTROL FILE                          0                         0               0

REDO LOG                              0                         0               0

ARCHIVED LOG                          0                         0               0

BACKUP PIECE                       1.79                         0              20

IMAGE COPY                            0                         0               0

FLASHBACK LOG                         0                         0               0

FOREIGN ARCHIVED LOG                  0                         0               0

7 rows selected.

Googled and found below in http://www.allinterview.com/showanswers/41216/ora-19806-cannot-make-duplex-backups-in-recovery-area.html

this is because you might have set the parametes
1)configure datafile backup copies for device type disk to
2)configure archivelog backup copies for device type disk to

now the solution is to clear the above two configuration
settings i,e...
A)
1)configure datafile backup copies for device type disk to
clear;
2)configure archivelog backup copies for device type disk to
clear;
now it will work ................... 

Tried to reset back to 1 copy, and it did works for me now. 

RMAN> CONFIGURE ARCHIVELOG BACKUP COPIES FOR DEVICE TYPE DISK clear;

old RMAN configuration parameters:

CONFIGURE ARCHIVELOG BACKUP COPIES FOR DEVICE TYPE DISK TO 2;

RMAN configuration parameters are successfully reset to default value

RMAN can duplex backups to either disk or tape, but cannot duplex backups to tape and disk simultaneously. When backing up to tape, ensure that the number of copies does not exceed the number of available tape devices. 

This is could be related to I am using FRA as backup destination.