The discs may need to be "finalized" whilst they are in the Zenith recorder.
Put each disc back into the Zenith, then use the menu system to find "Finalize Disc".
Finalising a disc is necessary to allow playback of video content on a device other than the device that the video recording was made on.
I am 99% sure that the disk was finalized on the zenith.
The key thing is that the disk DOES play on my son's Alienware laptop.
It is not even recognized by the drive on my ASUS laptop or another Dell desktop.
All machines are set for Region 1 (USA).
I can't figure out what magic mojo the Alien has.