SQL & PL/SQL :: ORA-04089 / Cannot Create Triggers On Objects Owned By SYS

now i can log in but here i faced with another erorr, while i am creating a trigger it gives the following erorr:

SQL> ed
Wrote file afiedt.buf
1 create or replace trigger trgr
2 before insert on myTable
3 for each row
4 begin
5 select mySequence.nextval into :new.ID from dual;
6* end;
SQL> /
create or replace trigger trgr
*
ERROR at line 1:ORA-04089: cannot create triggers on objects owned by SYS

note: i tried and gave different names for the trigger, still it is the same.