Suddenly within the last week or so in LR Classic (7.2), Library mode, I cannot move a sub-folder with photos from from one folder to another. I get an error, "Could not complete the folder move. An unknown error occurred." It doesn't matter if it is a newly created folder or an old one. I also cannot rename a folder. The catalog has been optimized, PC (Win 10) rebooted, 12GB RAM and usage is 65% of that RAM.
As an example, I can create a sub-folder "B" inside folder "A". I can create another sub-folder "C" inside "A". I cannot move B into C or move any of them to another folder. I can create and move empty folders, but if it has an image in it, it can't be moved around. I can move images from B into C, but I can't move folders.
My workflow is easiest when I move folders and I've been doing it this way for over a year. I don't know what may have changed. I'm looking for ideas so that folders can be moved or renamed in LR. I can close LR, go to Explorer, move the folders, reopen LR and then "find" them for the directory but that is not what should be required.