System has not been taken off maintenance mode completely.
I started the database instance and listener on db tier. I also started the application service on the app tier. Then, I ran adadmin to disable the maintenance mode.
The query from db shows:
SQL> select fnd_profile.value('APPS_MAINTENANCE_MODE') from dual;
FND_PROFILE.VALUE('APPS_MAINTENANCE_MODE')
--------------------------------------------------------------------------------
NORMAL
Then, I went to the web login link and logged in as sysadmin.
However, after I logged in, there is a warning message displayed on top saying that the system has not been taken off maintenance mode completely. Please contact your system administrator.