Any artwork or such is copyrighed to the creator, doesn't matter if it's a mod of the game, aslong as they made it from scratch all meterial are their property and permissions from those iduviduals is needed to be certain you're cleared. Just to clarify
Sounds like you're missing som image files or something in your install when you get red x'es?
expantionpacks missing perhaps? (it was after all about 4 or so years since i last played any Nova games so I'm kinda guessing here
)
Hmm regarding copyright, unless Novalogi has a paragraph in their license agreement that makes everything made for the game such as mods an simular falls as property of Novalogi, haven't read their agreement so it is a possability and then you'd only need N Inc's permissions