[Dan C.]

"Integer Overflow" implies that it's seeing a number somewhere that's bigger than it can handle. Check your modded file for typos involving large numbers.

Thanks, I looked through but I didn't see any particularly large numbers, but I'll have to look again. The strange thing is that it occura halfway though player placement, not in reading the files in the first place, I assume it is selecting a world, upgrading it to the start conditons and then placing the facilities on the world. I can't think what could be too large a value there...