I know this thread is extremely old but I just wanted to say a huge thanks to Dave for those links! You're a champ for working out that!
I had a problem with a HD in which I was not able to access the files on 1 partition for some reason and had no idea why.
but after checking out those links, everything went back to normal again which surely is a relief as I was thinking about formatting the drive which contained data I had not backed up yet.