File or folder open in another program

Problem

When I try to delete a folder or a file in Windows Explorer, it gives me this error:

Folder In Use

The action can't be completed because the folder or a file in it is open in another program.
Close the folder or file and try again.

Solution

This error means that some Windows program has opened the file I am deleting or a file inside the folder I am deleting. Sometimes, I know which program that is and I can close that application. When the application is closed, the operating system typically closes all the files that were opened by that application, so the problem is resolved.

But usually, I do not know which program has opened the file. And even after I close all the program windows, the error persists.

This means that some background process that has lost its window has this file open. We need to find out that process and kill it. I usually use the find feature in Process Explorer to do this.