My won't the switch change?

I wrote a scenario that worked fine, but used a P42 engine on the Northeast Corridor. I've been getting requests that people want to try it, but cannot since they do not have a P42, which is currently not available on Steam. I decided to update the scenario using an AEM7 and leave everything else the same.
The big problem that I am having is when my train is on the northbound fast track, and passes a train stopped at a red signal on the slow track. The driver train is then to switch over to the slow track. The path shows correctly on the HUD. I enter the switch and start to change to the slow track. As soon as I hit the switch half for the slow track, I get a "train derailed due to switch set against train" error.
- Why does the second switch in the interlocking pair set differently than the first switch
- Why does it work in one scenario but not another
- What can I do to fix this?
The big problem that I am having is when my train is on the northbound fast track, and passes a train stopped at a red signal on the slow track. The driver train is then to switch over to the slow track. The path shows correctly on the HUD. I enter the switch and start to change to the slow track. As soon as I hit the switch half for the slow track, I get a "train derailed due to switch set against train" error.
- Why does the second switch in the interlocking pair set differently than the first switch
- Why does it work in one scenario but not another
- What can I do to fix this?