A developer reported a weird error ORA-0131 when he connected to the database in PL/SQL developer.
In fact, there's no ORA-0131 such error in Oracle database. I think it's a typo of ORA-01031: insufficient privileges.
To enable users to call DBMS_DEBUG in their session time, we have to grant DEBUG CONNECT SESSION privilege to the users.
SQL> grant debug connect session to scott;