I specified a scenario and made sure that all relevant parameters for the models I'm generating predictions for are specified.
Now - for the first time - I got an error message I can't make sense of as I replicated a scenario, adjusted it and tried to run the simulation.
"Assigned level values must be either ascending or descending"
I went ahead and retyped the relevant levels and deleted all empty variables again to make sure there aren't any spaces or unusual characters in there. No luck.