Hello, first off I would check the plugins folder and check to see if there are two unsharp mask files there. I would cut one file into another folder and then try it out and if it screws up on you, paste it back into that folder and try the other one. Also do you have any plugin manager software? If you do, the unsharp mask might have been copied within that. The only other thing I can think of is that the Nikon software put a bad copy of that filter in your ps6 directory somewhere because unsharp mask is a common filter used with digital imaging and scanned pictures.
Hope this helps!