I just checked forts and the crashing part is commented out (gee, I wonder why). No help there. I just tried to disable the code and sure enough the crash is avoided. However instead it asserts in doTurn because there is a city without a plotgroup Something is not right here. At least it tells that it was correct to fill in asserts as it would otherwise have crashed in a different location and the average player would think it would still be the same crash.