Sometimes you try to empty a folder or delete a file only to find out you can’t because something else is using it. XKCD pictures it like this:
Sometimes you think you have everything closed yet you still get this message. You may need to restart your PC to make sure all instances that may have been previously connected to it are now disconnected. Another thing you can try is a program called LockHunter. Once it’s installed, you right click on a folder or file and you will see “What is locking this folder?” or “What is locking this file?”
After you click that, you will see what is locking the file or folder. I right clicked on a Pictures folder and clicked “What is locking this folder?” After that, this came up:
I can now find out what is locking the folder and take the actions I need to try to remove it.