The default sleep settings in OS X 10.7 (Lion) and 10.8 (Mountain Lion) cause the Mac to go to sleep while running a backup (either manual or scheduled) or a restore. They also prevent a Mac from waking up for a scheduled backup.

Formerly, there was a workaround required to configure a Mac for backups and restores but this has been addresed in recent versions of the client. If you are running OS X 10.7 or 10.8 (Lion or Mountain Lion) please download the latest client.