Thanks for some ideas. Sorry, should have explained more, nothing quite as complex as you suggested.
I have just updated to MC20, and afterwards uninstalled MC19. All music playing etc. works fine.
I am attempting to carry out a little housekeeping on some new flac files, just manually updating a few of the tags, composer etc. To do so I am using the Tag command from within the Action Window.
When I have changed the composer tag, then MC shows that it is updating tags.
After this, if attempting to change another tag in the same file, or to locate the original file on disk, then MC complains with an error, of the form "Media Centre encountered errors whilst tagging or moving files, check that files are not read only or open by another program"
Looking at the folder of flac files, it is apparent that the filename has been updated with a (n) - where n is the most recent number version of the file. Repeated attempts to update tags will result in (n) increasing !
I don't know how MC works, but it is almost as if MC holds the original file open, then tries to write the new file to the same filename, Windows7 doesn't allow, but updates the file number version. MC writes the file then closes/deletes the original, leaving only the filename with an incremented version in (). I'm sure this is not what is happening, just my explanation of a possibility !
The files are held on a Synology NAS. MC on a dedicated media pc, Windows7, MC20.0.17
Thanks
Phil.