When a scheduled, or manually initiated, backup is complete (I think!), the display indicates "Last backup: none" and "Last backup status: Last backup was successful"
Is the "none" an error, or does it indicate that there were no changes to the "mirror" backup. I would expect that there should be a few files changed.
Incidentally, an earlier query regarding FBackup not running as scheduled, appears to have been fixed by the recent update.