I just have to give a honourable mention to Unlocker, a freeware software program that really is indispensable. Many is the time when I was ready to smash the computer in frustration but then Unlocker the Cavalry came riding to the rescue in the nick of time.

Basically when you open a file, whether it be an image, a document, whatever, many computer processes will be used to open that file, run it, and do whatever you need to do to it. When you close that file, those computer processes may still be running and so you will be unable to delete, move or rename the file until those processes have been shut down. This is where Unlocker comes to the rescue because by this point your blood pressure is starting to rise and you're giving serious thought to starting a new career as a serial killer.

If you get the above error message, then just right-click on the file and choose the "Unlocker" option. You will then get a pop-up window giving you details of the processes holding the file in place and an option to kill those processes. If you decide to kill the processes, you can do so at the click of a button and the file will instantly be free so you can delete, rename or move it. What a lifesaver!