How to extract the OS password specified for scheduled remote external job IN oRACLE 11.2.0.4 ?

How to extract the OS password specified for  scheduled remote external job IN oRACLE 11.2.0.4 ?

SELECT u.name CREDENTIAL_OWNER, O.NAME CREDENTIAL_NAME, C.USERNAME,
  DBMS_ISCHED.GET_CREDENTIAL_PASSWORD(O.NAME, u.name) pwd
FROM SYS.SCHEDULER$_CREDENTIAL C, SYS.OBJ$ O, SYS.USER$ U
WHERE U.USER# = O.OWNER#
  AND C.OBJ#  = O.OBJ# ;

ORA-00904: "DBMS_ISCHED"."GET_CREDENTIAL_PASSWORD": identificativo non valido