I was logged in as SYS and trying to remove a job but was getting the following error :

SQL> execute DBMS_JOB.REMOVE (141);
BEGIN DBMS_JOB.REMOVE (141); END;

*
ERROR at line 1:
ORA-23421: job number 141 is not a job in the job queue
ORA-06512: at "SYS.DBMS_SYS_ERROR", line 86
ORA-06512: at "SYS.DBMS_IJOB", line 529
ORA-06512: at "SYS.DBMS_JOB", line 171
ORA-06512: at line 1

Then after some reseach, I found how to remove the job that is owned by another user:

SQL> EXECUTE SYS.DBMS_IJOB.REMOVE (141);

PL/SQL procedure successfully completed.

Hope this helps.

Thanks,