SQL & PL/SQL :: How To Delete ORA 00604

this is my trigger..SQL> create or replace trigger drop_trigger

2 before drop on database
3 declare
4 PRAGMA AUTONOMOUS_TRANSACTION;
5 BEGIN
6 INSERT INTO ddl_log
7 SELECT ora_sysevent,ora_dict_obj_type, ora_dict_obj_owner,
8 ora_dict_obj_name,USER,SYSDATE,to_char(sysdate,'hh24:mi:ss')
9 FROM dual;
10 commit;
11 raise_application_error(-20090,'you can not drop');
12 end;
13 /

DÚclencheur crÚÚ. when a user enter a "drop table" for exemple, the trigger is run but we have this error message

SQL> drop table fg;
drop table fg
*
ERREUR Ó la ligne 1 :
ORA-00604: une erreur s'est produite au niveau SQL rÚcursif 1
ORA-20090: you can not drop
ORA-06512: Ó ligne 9

what can i do to delete the ORA-00604??