Yes, this is FSO choking on a feature that's only available in newer builds. You can play pre-19 with MVP 3.8, and you can play all MVP versions with 19 and up, but you can't play all MVP versions on pre-19.
To switch builds, you will need to update Knossos to 0.14 final, enable "show FSO builds in list", update FSO, and finally select the newer version of FSO.
Someone should edit demo-wep.tbm and change model for Shivan Bomb from belial.pof to S_Bomb.pof
These flying sentry guns...