ora-00030 user session id does not exist

Recently, I got the error message

ora-00030 user session id does not exist

when killing a session with ALTER SYSTEM KILL SESSION ,

In v$session, the session was visible as ACTIVE, so why is the user session not existent?

The solution: Keep in mind, that you are connected to the correct node when using a database RAC. In my case, killing the session was only successful on the instance of that session. Look the node up using this statement:

select s.sid, s.serial#, i.host_name, s.username from
  gv$session s join
  gv$instance i on (i.inst_id=s.inst_id)
where
  username is not null;