SYS.SCHEDULER$_EVENT_QUEUE

- ORA-04020: deadlock detected while trying to lock object SYS.SCHEDULER$_EVENT_QUEUE
ORA-06512: at "SYS.DBMS_ISCHED", line 7761
ORA-06512: at "SYS.DBMS_SCHEDULER", line 4063

Solution: try to run the same sql statement ( DBMS_SCHEDULER.ADD_JOB_EMAIL_NOTIFICATION ) as user sys.