On a PC there are underlying code mechanisms to verify and play BR media and Kodi will leverage those frameworks. There is no equivalent on Linux (there are no Legal or certified players for Linux) hence libaacs exists and attempts to plug the gap. Unlike Windows where everything just works, libaacs depends on someone making the effort to dump the keys for a disc and submitting them to the database
Thanks chewitt, I appreciate you taking the time to reply and explain the difference as to why it might be working on windows. I'll keep trying though. I've put in 25 blu rays now and all have failed!!!!!! Do you think it's worth my trying a clean build too? I haven't done a clean build for a couple of years, just been upgrading from my existing one.