ORA-02391: exceeded simultaneous SESSIONS_PER_USER limit

1. Check how many sessions were existed:

SELECT count(*) as connections, username 
FROM   v$session 
GROUP  BY username 

ORDER  BY username; 


2. Check SESSIONS_PER_USER for the user: (example username: THONY)

SELECT a.username, b.profile, b.resource_name, b.limit 
FROM dba_users a , dba_profiles b 
WHERE a.profile=b.profile AND b.resource_name='SESSIONS_PER_USER' AND a.username='THONY';


3. Alter SESSIONS_PER_USER value: (example profile: DEFAULT)

ALTER PROFILE default LIMIT SESSIONS_PER_USER 10;