[SOLVED] Cannot Delete .Iso file.

I have a .iso file that I'm trying to delete, and I can't. When I try to delete it, it tells me "The action can't be completed because the file is open in System. Close the file and try again."

I can't close System, so I can't delete the file. The file is not mounted. I've tried downloading Malwarebyte's File Assassin, but that too told me that it could not delete the file. What's going on?