This was flagged as neglected since no other experts have responded. I'll try to help a little but I've never messed much with OEM and management jobs so it won't take much to get over my head.
I suggest trying the same 'case' in both commands:
execute sysman.mgmt_jobs.stop_all_executions('BACKUP_PRIMARY.CSUHAYWARD.EDU_000011','SYS');
execute sysman.mgmt_jobs.delete_job('BACKUP_PRIMARY.CSUHAYWARD.EDU_000011','SYS');