For the love of god, map makers, please do not place any scaffholding 6 on your map.

Unless your cursor will only point places with a close ceiling, that scaffholding from hell (literally, it's the chains from hell) will make your game crash. I guess the game tries to calculate the highest point to which the chain can hold to, a point which doesn't exist when you don't have any ceiling...
This has already lost me a couple of map making hours, please do not make my mistake and quicksave your map regularly.