I found my copy of the original installation files for Fort Smith to Heavener, so I bought only the new scenarios pack from Allaboard. While waiting for the download codes to arrive, I installed Fort Smith, which I had removed at some time in the past. After downloading the Switchin' Is Railroading pack and checking its readme files, I installed it (I'd already installed the required ALCO-S2 and its fix). Scenario 19 (the pack's 1st) ran successfully (but see notes below about route), but not scenario 20.
Scenario 20 problem: all well through the 2 pick-ups and the run to Howe, but then the drop-off at Howe resulted in a failure message. This d/o involves dropping the cars from the second p/u, which are designated in the instructions by a consist number, with no numbers provided for the cars that make up that consist. The consist, of course, cannot be identified by its number while running the scenario, but I'm 100% positive that I dropped the correct cars. Having saved the scenario just before the drop-off, I quit and resumed, but the drop-off still failed. RATS!!!!
Fort Smith route problems:
1) while running scenarios 19 & 20, lots of those obnoxious "walls" popped up and vanished: black walls, tan walls, corrugated grey walls; some horizontal, others vertical.
2) lots of abrupt lighting changes, which I seem to recall as being related to the sky dome used in this route.
3) quite a few of those "milk bottles" that indicate missing assets alongside the tracks -- probably some bit of scenery.
At this point, I am not a happy customer!
EDIT:
I looked at scenario 20 in the Timetable Editor. The first pick-up instruction includes cars 30215, 30483, 30915, 31527, 31374, 31398. The second pick-up instruction includes cars 30215, 30483, 30915, 31527, 31374, 31398, 686377, 31443, 31838, 204748, 202071, 218204, 224381. These are followed by a drop-off instruction that includes all of the cars required in the second pick-up instruction.
So, the player is instructed to pick-up cars 30215, 30483, 30915, 31527, 31374, 31398
twice! This might well make the drop-off instruction impossible to complete successfully. I'll try resuming the scenario form the train's arrival at the drop-off marker and see what happens.
In my opinion, the use of "consist numbers" that do not reveal the car numbers contained in them is not a good idea.
2nd EDIT: dropping all cars where instructed did the trick, allowing me to complete the scenario successfully. The use of consist numbers potentially creates confusion, however, and reinstalling the route did not remove the walls and bottles:
Walls:



Bottles:
