Right! I added a note to the Steam version warning players not to load any mods with Faerun. I've changed too many things, so compatibility is out the window... There are three exceptions that I know of: IGE, IfoAddict, and my Greatest Cities. My guess is that you were trying to build a specific wonder that requires some feature (a river) or minimum population or religion. There are a few of those! Great! There are no upgrades between differently powered units -- you'll have to build the higher tiers from scratch each time. They are generally worth giving up all the promotions of the lower tier units. The main upgrades to consider are the races.