I thought something along the lines, but we must be doing something different because the default setting for Trigger is None (also Autorun, Parallel Process available) but Conditional Switch won't let me pick "None", only variables. However, according to the tooltip (assuming it's working correctly) the Switch is only paid attention to if the Trigger isn't set to None.
("[None] starts only when explicitly called up.")
So, (again, assuming the engine is working properly) the conditional switch is never even looked at.
I checked the working event I mentioned was done the same way and it does have the same set up, so I don't think that's it.
I hope it's not a script incompatibility, but the error states that something is undefined, and I haven't seen that one before.
EDIT: And the plot thickens. It seems it might be something saved into the game save files, as I tried a new game and had no problems, but even loading a certain save gave me the error. I'm going to try to play a new game until I can save without calling any choices, then save, load, and try again.