Took from fsdreamteam folder in FSX the file called GreystoneX and put it into the file named Addon Scenery in FSX.
Sorry, it wont work this way. You left the files were they are, and simply go into your Scenery Library, and add a new Area for Greystone, by browsing the folder were the scenery is, which is fsdreamteam\greystonex (or 17fl, not sure), you give the area a proper name, and restart FSX when prompted.
Pay attention to either restore the file as they were now that you moved them or, remove the folder in Addon Scenery and reinstall the scenery.