I finally finished the session, the problem started with driver Bald. His train would derail every time while he was navigating Quinnimont yard. I was able to avoid this by switching to his train and giving the driver a maximum speed rule that I set to 25 mph.
Then the next problem showed up. Driver Andrew was given orders to drive to Cliffton forge, which is a "portal basic short" which was supposed to remove his train from the session when he went through it. for some reason the portal wasn't working and so Andrew just crashes into the end of the map...derailing. I got around this problem by changing his orders, stopping his train before the portal.
This route/session is built-in content in Trainz a New Era. I'm not certain if the route was in earlier versions of Trainz