Name was changed

Try using job number, change name again, use wildcards

Username was changed

Use /USER= or "name=user" format for access

Job had /NORETAIN set

Run VSS_REPORTS to check for deletion

Someone deleted job

Run VSS_REPORTS to check for deletion

VSS.DAT was restored from a backup file

Old database from before job was created --CREATE job again

Looking on wrong machine

Check other machines, or use of /SERVER

NSCHED$DATA logical pointing to wrong database

See system manager