Unlocker

Ever had such an annoying message given by Windows?

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.

http://www.emptyloop.com/unlocker/#description