I rebooted my PC that records television this morning.
At that point, the hard drive which is specified in Television as the location for recording, was not connected (I had disconnected it to use the USB connection for a one-time backup).
I had left myself a note to connect it up prior to the start of the next scheduled recording, and did so. I checked in Windows Explorer and the drive was present and available.
But the recording did not occur.
It has previously occurred without problem (a daily recording rule), so it seems likely to have been due to the disconnected hard drive. So, I am guessing that it checks for the existence of the recording folder on startup, perhaps? (Rather than at start of the recording?)