Unlocker application was designed to be a very useful Windows Explorer extension allowing users with a simple right-click on a file or folder to easily get rid of error message such as error deleting file or folder, cannot delete folder.

It has many other flavors:
Cannot delete file: Access is denied
There has been a sharing violation.
The source or destination file may be in use.
The file is in use by another program or user.
Make sure the disk is not full or write-protected and that the file is not currently in use.