u mňa takúto situáciu spôsobovalo scanovanie antivírom na pozadí...
Zistil som to vďaka "Unlocker"-u, ktorý slúži práve na podobné prúsery... viď nižšie

http://www.softpedia.com/get/System/System-Miscell aneous/Unlocker.shtml


If you've ever been unable to delete a file in Windows, and can't figure out what program's using it, Unlocker is the solution. Have you ever seen these Windows error messages?

Cannot delete folder: It is being used by another person or program
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.

Unlocker can help! Simply right-click the folder or file and select Unlocker. If the folder or file is locked, a window listing of lockers will appear. Simply click Unlock All and you are done!