"Unit is locked"

[screamingstrat]

I am trying to mount an .ISO image, but whenever i try, Daemon Tools responds with the error message: "Unable to mount image: Unit is locked."

what makes it "locked" and how can i fix this?

[Copytrooper]

Figure out which program sends lock drive request, usually some game exe still running in background due to buggy protection - end related process via task manager, then try again.