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.