I have problem dropping a user from the database.
drop user "USERA" cascade;
This gives me the following error:
ORA-01940: cannot drop a user that is currently connected
But when I check the v$session table, I cannot see USERA connected to the database.
ALTER USER usera ACCOUNT LOCK;
Come back in a day and the user will not be logged in, most likely. You should be able to drop the user. Or wait until you bounce the database and then drop the user shortly after startup.
I have to add that if USERA is connected to the database, then dropping that user will break someone's application. Make sure you really want to do this before proceeding.