The chest got me the first time. Alas it seems there is something else on the map that will cause the error- all I can think I did differently was picking up and replacing a lot of the existing train rail. I have the same issue as the other posted originally in this thread. This map is like a double...

I get the same error, third attempt on New Hope 2.

This is around 2 hours in this time- It's either the above error or the deserialisation error on the earlier saves.