This is not a build issue, but related to the registry of the original game* And the reaction of FT_Improver to this... The mod can be run using URM_W9X (used bos.exe instead of improver) About error: Spoiler *I came across the fact that the GOG version number 126.96.36.199 has crooked registry values. Improver does not work with this version (and hence mods too) and complains about a "broken" registry. Uninstalling Deleting in the usual way and replacing it with another version of the game does not help. You need to clear the registry from mentioning FOT. And only then, install another version and mods. Perhaps there are other versions with the same problem, but GOG (actual), Steam & EGS versions, should work fine. If the game is installed in C:\FOT (or any other way except PF), then the mod is installed in the same directory i.e. C:\FOT. Just checked, it works fine.