ORA-01093: ALTER DATABASE CLOSE only permitted with no sessions connected

SQL> select switchover_status from v$database;

SWITCHOVER_STATUS
--------------------
SESSIONS ACTIVE

SQL> select SID, PROCESS, PROGRAM
2 from v$session where type = 'USER' and
3 SID <> (select DISTINCT SID from v$mystat);

SID PROCESS
---------- ------------------------
PROGRAM
------------------------------------------------
1 20494
sqlplus@dg2 (TNS V1-V3)

SQL> alter database commit to switchover to primary WITH SESSION SHUTDOWN;

Database altered.