imperialmog,
Do you have BUG installed over your core civ files? If so, this may be the cause. I found that while I had BUG installed I could not play space Civ mods and Age of Ice.
To remedy this you need to remove BUG from your core civ files.
I was able to accomplish this by uninstalling BTS, removing my /Program Files/.../Beyond The Sword/ folder, removing /My Games/Beyond The Sword/ folder, then reinstalling BTS and BUG as a mod. I'm not sure if I took extra unnecessary steps or not, but I was able to solve the problem.
(If you have data you wish to save in those folders to "remove" them you can simply rename them to "Beyond The Sword.old" or move them to another location on your hard drive.)