I had this problem and successfully used the idea of moving and/or incrementally deleting items.
I could not move a folder with two sub-folders and files. It was an old folder, so there was no way anything imaginable could have been using it. I used resource monitor ("search" box, above right section of the handle-and-file sub-window under CPU activity) to verify that the Explorer process window did have something associated. The ONLY process associated with them was the display window (Explorer) and they seem to only have been there because they were within the list of folders being displayed. No other processes were active.
Otherwise, there were no active processes using these files or folders. I checked for lock files or other odd things like hidden or system files and there were none. The command prompt didn't help. Each item had the same name, and I could not move the parent folder in DOS either. NOTHING seems to explain why I could not delete the parent folder, so obviously my knowledge of the intricacies is deficient.
I managed to use Windows Explorer to move each folder's files to another folder (even used the same folder names, but did not copy the name in case an invisible character was there). After moving files, I deleted the folders. Then I put them all in a duplicate file structure right where the old one "was", to see if I could (I could). Finally, I moved the folder (and contents) to its intended new destination. I'm happy! :-)