Oh no! That bug rears its ugly head again.
I'm afraid this is a bit of a known issue on the EL Geeps though it doesn't seem to affect everybody. My best guess is that there's a cross-reference hidden somewhere among the files that links to one of my other Geep packs, which causes this issue when those other Geeps aren't installed.
Do you have any of the other Geep packs installed? Could you give that a try if you don't? Especially the GN pack would be of interest.
Cheers,
Michael
Edit, PS: also, please double check that you've activated the "Kuju\RailsimulatorUS" assets filter in the scenario. It's needed for the sounds.