Also, is there a reason that you have set up two independent libraries
greetings -
in my original post, i misstated the situation, which affected the answers i was given.
mea culpa. mea culpa. mea culpa.
i stated that the PC and Mac libraries were imported from the same music folders on my NAS. that's true, as far as it went. what i should have added, is that, i run both PC MC and the Mac MC using that same common library, which is also on my NAS. this doesn't work, as far as i can see.
for those who replied to my post, you probably realized that the message talking about 'database being open for read only' was coming from my NAS OS, rather than from MC i didn't grok this fact for awhile and once i did i tried an experiment. i reversed the order in which i started MC. usually i start it in the PC and then the Mac, which results in the Mac having the 'read only' message. starting on the Mac first and then on the PC results in 'read only' message being on the PC.
well and good, but guess what! the library on the PC is now screwed up in the same way as on the Mac (albeit involving different albums), with missing cover art and multiple entries for albums with various artists. to add to the injury, the common library is now irredeemably messed up on both the PC and Mac. no amount of MC restarting, or library re-importing, or machine rebooting will fix this. i hadn't look at my movies under MC, in a while. when i did i found they were also screwed up, although in a different way. for movies, i have double entries for every movie. this difference in the way they are screwed is probably because my .mkv files don't have tagging abilities.
i don't know the layout of your library database, obviously, but i suspect this whole fur ball is the result of trying to share a library with machines running two different OSes and the different ways the OSes name their folders. so be it.
luckily, i never deleted my original 'Main' local library on the PC. i have fallen back to that version which is mostly intact and is set to auto-import from the always-the-same music/movie folders. since i use a syncing program to sync my music folders to Amazon's S3, i.e. over the internet, i save all my cover art in the folders, rather than the music files. in this way, i avoid unnecessary, extended uploads should the cover art un-explainably change. this has happened, although because the cover art is in a NAS file that is also shared by multiple OSes, i suspect that will never work either.
do you think multiple OSes are the problem? my guess is that, since my situation is relatively unusual, this approach and its seemingly attendant problems have never occurred to you to consider. something to keep in your hip pocket.
of course, the solution to this is to use the client-server approach. i originally tried this before anything else. i, for some reason, found it inadequate. i don't remember why. i may simply have been tangled up in my shorts.
since the 'Main' library on the PC is relatively healthy, i plan to use the PC as server and the Mac as client. once i do this i may remember why i rejected this approach in the first. if so - to be continued, otherwise - no news is good news.
regards