Sony RDR-VX525 DVD Recorder / VCR Combo

I copied two VHS tapes to DVDs on this machine. The DVDs play back on this machine, but every other DVD player I tried failed to play them, including another Sony DVD player which displayed a "no disc" error. I also couldn't play them on my computer, and I tried a variety of software DVD players and DVD ripping software. It is not a codec issue. One DVD burner program was able to tell me that the DVDs contained 1 session with 2 tracks, with the second track (judging by its size) containing the video/audio data. This is not any kind of standard format. It's useless if you want to play the DVDs on any other player, or on your computer.