Here is what I think is wrong. Click this link to see if it matches your problem, and then read post #15 for the solution.
http://forums.civfanatics.com/showthread.php?t=470236
You must check to be sure that the Mod is in the BTS/Mods folder and not present in the "My Games" folder. Check your My Games folder on your computer. It will probably be in a folder named whatever your username is on your computer. It is probably in the same folder as your "My Documents"
In the "My Games" folder, there should be a folder that says Firaxis or Steam, then a Folder for Civ 4 then BTS. In the BTS folder there is a Mods folder. The Mod must not be in this "My Games" folder or any subfolder of "My Games". The Mod must only be in the C:/Program Files/Firaxis/Civ4/BTS/Mods folder.
Another thing it might be is that you have the Blue Marble add-on or something else in your "Custom Assets" folder. Remove it and the game should work. Click this link to see if it matches your problem and read post #7 for the solution.
http://forums.civfanatics.com/showthread.php?t=233874
The last thing I have seen is that Norton Antivirus causes the problem and that uninstalling then reinstalling Norton fixes it. Here is a link:
http://realmsbeyond.net/forums/showt...d=5586&page=11 Read post #104 to see if it matches your problem and post #106 to see the solution.