After the Donner Pass Update only a couple Scenarios would start without problems. Most failed to start, listing some rolling stock not loaded.
I tried the usual cache verification but that didn't fix it; the step that solved it was clearing the cache.
1 Main Menu
2 Game Settings
3 Tools
4 Clear Cache
All the listed Scenarios for that route now load. Much improved route, very impressive for a freebie update! :-)
GaryG