"Oh yeah, that one wouldn't play either." At least they were nice about it.
Potential problems filtered though my head. I checked the file structure of the image I kept just in case and it seemed okay; I had tested the DVDs (both of 'em) on a stand-alone player here before sending them and both worked, so I was stumped. A few more rounds on the phone and just out of pure curiosity I asked what they were trying to play it on. "The lobby dvd thing there." Okay, almost helpful. So I decided to ask the exact model number of the player they were using mumbling something about "firmware" and pretending to be interested in some obscure facet of DVD Player technology they couldn't possibly understand.
Googling the model number of this player revealed it was older than some stromatolites which inexorably started me falling down the WikiHole™ until I discovered this little tidbit of info:
The AUDIO_TS folder is there for backwards compatibility with older-than-dirt DVD Players even though it's used for DVD Audio Discs (sometimes called DVD-A discs) which hardly anyone one makes anymore.
Wha? Yup, their DVD Player was so old that it required an AUDIO_TS folder on a video only DVD. Silly me had not included one because I had never needed one before in the history of me burning DVDs for clients.
So lesson here is to really never underestimate client's hardware.
If they have any:
"Yeah all of our employee laptops have DVD players in their laptops."
Oh, okay great, I'll make 1000 copies for you guys by the end of next week."
"No those are CD-ROM drives, not DVD Players in your employee laptops. Where's my check?"