Cannot copy xxx: It is being used by another person or program. Close any programs that might be using the file and try again.

I am trying to copy/delete a file from hard disk and I have got the following message:

"Cannot copy xxx: It is being used by another person or program.

Close any programs that might be using the file and try again."  so I searched and googled it and I find a utility called "unlocker 1.8.8" and it solves my problem  , run unlocker then select the file/folder you want to copy/delete/move and select the action you want ..and unlocker will handle it for you , and I used it to copy youtube videos from temporary folder which they have names like "flaC45.tmp" for firefox .