NOTE: I haven't used this stored proc (nor the job scheduler) so I don't have any solutions ... just questions and a suggestion ...
Does the 'plancost' option work for any other queries?
Does the 'plancost' option work in any other dataservers?
You could try troubleshooting the proc and the job scheduler or, since this is a Sybase-supplied proc, try opening a case with Sybase tech support.