Hi @sam62990
Have you tried different DL dvd discs just in case the one you're trying is faulty for whatever reason?
DL dvd discs aren't mentioned in the [https://manuals.playstation.net/document/en/ps3/current/video/video.html|user manual > video category] so the player might not support them.
This [https://www.avsforum.com/threads/ps3-cant-play-dual-layer-dvds.1106819/|link] may be of interest as it shows that others have had the same problem and managed to get some DL discs working.