Thank you. I searched the Monterey section and couldn't find this topic.
I never realized the "prevent hard drive from sleeping" option applied to *networked* time machine drives. This particular message never appeared in Mojave. I've had infrequent seemingly random "backup couldn't be completed" errors in Mojave, though.
The mini running Mojave with the time machine drive has always had "prevent hard drive from sleeping" deselected. It is also set to never sleep. It has no display, and I control it with screen sharing.
The "prevent hard drive from sleeping" option is not showing at all on my MacBook Pro, which is odd.
It is showing on the MacBook Air. It was selected on the Air, and I've deselected it.
Both laptop machines have 'enable power nap" selected under power adapter, which they are on when the errors occur, and that setting states that it allows time machine backups to run when selected.
We'll see if the Air stops throwing those errors, but any idea why the Pro doesn't even show the hard drive sleep option at all?