I have done a little more testing using the console to edit my army and see what works seems to load up the siege fine if i have only 1 infantry in my army just 1. But if i have a complete archer army mounted or not it crashes. i also tried attacking without siege equipment being built and it crashed aswell seems to not know what to do if you have a army consisting of archers solely and nothing else which admittedly is a odd play style but im trying a Mongol type play through using horse archers. So i guess i have to make sure i have atleast one infantry for now
