Why won't it let you use they were house key on Pokemon pearl?
you find it on the ground
The dusk stone is in the team galactic ware house. Once you get the key ( not works key, the storage key. ) There will be a small room before the stairs. go next to the computer and there will be a dusk stone. This can be used to evolve Misdreavus into Mismagius or it can be used on other dark types.
the key you got from the team galatic grunt dropped is not the one that's for the team galatic ware house you need to open the ware house door with that key and fight your way through it to find another key and that one is for the team galatic main building. You can get additional info here at the related link. (good luck!)