Sorry but I've yet to find Microsoft or makers to really address this head on. What does work is for me to log out and back in.
Did you also try end tasking Explorer in the Task Manager?
And about "release". When talking about Windows, try to use the lingo. That is, in Windows we Eject a device or drive.
Bob
Lenovo H420 Win 7 64 bit home
When I move the photo files to my local disk, after I finish and try to release the card, I am told that the device is currently in use. Even after opening Task Manager and closing all open programs, I am told this.
What is going on?
Roy

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic