Thanks for your answer. I don't know on what it is based. Here is the complete comment:
"a lot of dvd players do not like dvd-video made with +R single layer media. This is very well known. Customers buying +R for dvd-video usually use "bit setting" on their burner so that the disk reads as a "dvd rom" to avoid such problems. Not all burners have this feature though. If your burner is old, you may not have the latest firmware installed."
Checking on the CloneDVD forum, I see this comment that would go along with what my supplier is writing:
"For +R, +RW, and +R DL blank media, change the booktype of the blank media you're using to "DVD-ROM", if your burner supports bitsetting changes. This step improves the chances of playability in/compatibility with (standalone, mostly) DVD players. The best way to do this is through the software that came with your burner (if possible)".