I have tried everything with this and am sure it's something to do with codecs. No matter what I try it just never works.

I've tried several players (including VLC and Parole media) and installed all the libraries scattered throughout the advice out there but nothing seems to do the trick.

VLC just blinks and does nothing. Media player prompts "cannot access media".

Most 'interesting' message from dmesg :

[12941.476374] sr 4:0:0:0: [sr0] tag#0 Add. Sense: Read of scrambled sector without authentication.

Same problem in Lubuntu 17.10 and Fedora 26. Both new, clean installs.

Any help appreciated.

You need libdvdcss to watch dvds. You should get it from your repos or you can check the vlc website.

Thx Pete but I already did that and also have already got the following :

$ ldconfig -p | grep dvd
libdvdread.so.4 (libc6) => /lib/libdvdread.so.4
libdvdnav.so.4 (libc6) => /lib/libdvdnav.so.4

I also followed a "things to do after installing Fedora 26" guide of which DVD was a major part. This hasn't helped either.

On Ubuntu 17.10 I did the usual "restricted-extras" thing and that didn't work there anymore either.

I've checked the dvd region of the drive (using "regionset") and that correctly shows the region of "2".

This is driving me nuts when I should really be "fine tuning" Eclipse / Android Studio / Java .. etc... etc... etc...

... 20+ years of installing Linux and still get sidetracked every darned time !!!

dvdread != decss/libdvdcss.
You mention several distros...hard to give advice when we don't know what you're using now. But:
Fedora 26: "yum install libdvdcss" (note: may be libdvdcss2)
Ubuntu 17: "sudo apt install libdvd-pkg && sudo dpkg-reconfigure libdvd-pkg"

DVDread is for non-encrypted DVD's (few and far between: thank DRM for this). DVDCSS is the decryption library allowing you to decrypt the stream.

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Thanks TBOne, I think maybe something else is wrong then since the below indicates Fed26 'thinks' I already have libdvdcss.

And yes I'm trying both Fed26 and Lubuntu17.10 (as I flee full fat Ubuntu and it's cpu-hungry friend : 'c0mpiz').

----------------------
$ sudo yum install libdvdcss
Last metadata expiration check: 2:03:32 ago on Fri 17 Nov 2017 16:54:10 GMT.
Package libdvdcss-1.4.0-1.fc26.remi.i686 is already installed, skipping.
Dependencies resolved.
Nothing to do.
Complete!
-----------------------

Well strangely. It works now. I've done nothing else since to try to fix this.

So in the spirit of this forum I need to close this off with feedback by stating that I did nothing else other than to reboot my system and begin trying to fix it only to find that it already works now.

So my best guess is that either the reboot or unmount/remount of dvd actually caused it to start working (on Fed26 at least).

Thanks to TBOne and Petelq for their time.