ORA-00261: log 11 of thread 1 is being archived or modified

Try to drop standby logfile group, and get below errors. Because this standby logfile group is being used for real time standby database recovery.

SQL> alter database drop standby logfile group 11;
alter database drop standby logfile group 11
*
ERROR at line 1:
ORA-00261: log 11 of thread 1 is being archived or modified
ORA-00312: online log 11 thread 1: '/u02/redo/TESTDB/standby_011.log'

WORKAROUND

1)Clear standby logfiles:

SQL> alter database clear logfile group 11;

Database altered.

2) Drop standby logfile group:

SQL> alter database drop standby logfile group 11;

Database altered.

3) Add standby logfile groups, and enable recovering managed standby database.

4) Will see log shipping pauses with below errors :

*** 2019-01-21 15:11:39.944
Error 270 closing standby archive log file at host 'TESTDBSTY'
ORA-00270: error creating archive log
Archive destination LOG_ARCHIVE_DEST_2 made inactive: File close error
*** 2019-01-21 15:11:40.043603 4929 krsh.c
LGWR: Error 270 closing archivelog file 'TESTDBSTY'

5) Reset parameter “log_archive_dest_state_2” to wake up log shipping:

SQL>alter system set log_archive_dest_state_2=enable;