Quote Originally Posted by Squid
I can't help with everything, but you are missing a line from export_buildings.txt, you're missing a {orthanc_name} line (used in the building browser). Every building tree has the have a {building_tree_name_name} line.
well yes, I did it on purpose, because Orthanc tower is a unique building in the game, there is just one Black Tower of Isengard and its already built at the time the game starts, so there is no need to have it in the building tree browser.

BTW, I am deepening about overlays and underlays thing, but I see there are other buildings without any overlay-underlay floor defined in descr_settlement_plan.txt so I'm afraid its not that causing the CTD...

I just can't see what is wrong :(