Breakthrough: The memory error on exit is now fixed! It turns out that in Civ4LeaderHeadInfos there is a typo: FLAVOR_GROWTH was instead FLOVOR_GROWTH and civ didn't give an error on loading but instead had a memory error.
Cool! (How ever did you find that one?!)
@Azure-Dreamer: Sometimes unzipping a mod (or scenario) creates a folder inside the mod folder with the same name: BTS won't find it then. (If this is the case, rename the mod folder, like to "z[mod name]", cut/copy the folder inside to the Mods folder and delete the redundant z-folder.)