Hellow novacd,
how have you created your job?
I think your problem is like this:
you have created your job

VARIABLE Job_number NUMBER;
BEGIN
DBMS_JOB.SUBMIT(:Job_number,'Procedure_name', ...)
END;

try do it so:

VARIABLE Job_number NUMBER;
EXEC DBMS_JOB.SUBMIT(:Job_number,'Procedure_name', ...);

Is incredible, but it's true.
I had the same problem, and I resolve it so.