My host's support team was helping me with my CRON backup and fount this ticket #36049 which indicates that for CRON to work you must have the Akeeba Backup Console plugin enabled. The documentation for automated backup does not seem to mention the plugin. I would suggest providing a warning on the "Schedule Automatic Backups" page and also adding something to the documentation about this. It would have saved me a bunch of time!
Great product though, thanks.