Why does Deja Dup scheduled backup never run?

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http://askubuntu.com – I currently have a Deja Dup Backup utility in Ubuntu 12.04 to run scheduled backups every day but the backup never runs. The Overview tab always reports "Most recent backup: n days ago" and "Next automatic backup: Today". I can run a backup on demand no problem so as far as I can tell it's not a network availability issue or a permissions issue. It just appears not to run on schedule. Why? Also, the scheduled backup has never appeared to work for me, even in previous versions of Ubuntu. (HowTos)