RMAN-06820: WARNING: failed to archive current log at primary database

RMAN archive log backup at the standby site is throws the following errors

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RMAN-06820: WARNING: failed to archive current log at primary database ORACLE error from target database: ORA-17629: Cannot connect to the remote database server
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RMAN> backup database plus archivelog tag 'FULL_AL_BKP';


Starting backup at 29-FEB-16
RMAN-06820: WARNING: failed to archive current log at primary database
ORACLE error from target database:
ORA-17629: Cannot connect to the remote database server
ORA-17627: ORA-00942: table or view does not exist

allocated channel: ORA_DISK_1
channel ORA_DISK_1: SID=48 device type=DISK
skipping archived logs of thread 1 from sequence 192 to 201; already backed up
Finished backup at 29-FEB-16

Starting backup at 29-FEB-16
using channel ORA_DISK_1
channel ORA_DISK_1: starting compressed full datafile backup set
channel ORA_DISK_1: specifying datafile(s) in backup set
input datafile file number=00001 name=/u01/app/oracle/oradata/ORCLSTB1/system01.dbf
input datafile file number=00002 name=/u01/app/oracle/oradata/ORCLSTB1/sysaux01.dbf
input datafile file number=00005 name=/u01/app/oracle/oradata/ORCLSTB1/example01.dbf
input datafile file number=00003 name=/u01/app/oracle/oradata/ORCLSTB1/undotbs01.dbf
input datafile file number=00004 name=/u01/app/oracle/oradata/ORCLSTB1/users01.dbf
channel ORA_DISK_1: starting piece 1 at 29-FEB-16
channel ORA_DISK_1: finished piece 1 at 29-FEB-16
piece handle=/u01/app/oracle/backup/ORCLSTB1/ORCL_20160229_82_1_1.bak tag=TAG20160229T114824 comment=NONE
channel ORA_DISK_1: backup set complete, elapsed time: 00:00:45
Finished backup at 29-FEB-16

Starting backup at 29-FEB-16
RMAN-06820: WARNING: failed to archive current log at primary database
ORACLE error from target database:
ORA-17629: Cannot connect to the remote database server
ORA-17627: ORA-00942: table or view does not exist

using channel ORA_DISK_1
specification does not match any archived log in the repository
backup cancelled because there are no files to backup
Finished backup at 29-FEB-16

Starting Control File and SPFILE Autobackup at 29-FEB-16
piece handle=/u01/app/oracle/backup/ORCLSTB1/c-1424488411-20160229-05 comment=NONE
Finished Control File and SPFILE Autobackup at 29-FEB-16


But rest of the backup actually completed successfully.

As per the Source : http://oraclesivaram.blogspot.com/2015/11/rman06820-warning-failed-to-archive.html

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CAUSE:
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11.2.0.4 onward as per 'unpublished' Bug 8740124, we now include the current standby redo log as part of an RMAN archivelog backup at the standby site. This is achieved by forcing a log switch at the primary site. However, the connection to the primary failed when attempting to do so.This is due to this bug:
Bug 17580082 ACTIVE STANDBY RMAN06820: WARNING: FAILED TO ARCHIVE CURRENT LOG AT PRIMARY

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Workaround:
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Do not use operating system authentication to login with RMAN. Use a username and password.

That is, do not use just the "/" (operating system authentication) connect to the standby database:
$ rman target /
Connecting as 'rman target /'

# it gets the sys user but not the password and so, it does NOT mean it is being explicitly specified to connect as sysdba.
Instead put in the username and password for the SYSDBA user:

$ rman target sys/password@stby
Connecting as 'rman target sysdba_user/password@stby'

Note: Also make sure password, within the (ORAPWD) password file, in primary and standby should be identical.

For more details please look at the Doc ID: 1616074.1