OK, DL'ed and installed this latest you provided, but the error is still the same.
I think I should add that the files handled by MB are all FLAC, many with manually added tags, but only few of these are defined in MB.
Usually I work with Foobar2000 to handle tags and everything else. MB is used as catalog for organizing and finding things.
I still organize it all, so many HDD relocating may occur, as well as changes to tag values.
Each time I load MB, I perform re-scan of the relevant folders to sync the latest changes on the albums.
Does this help in anyway?