I've been trying to play scenario battles like Survival and Massacre, yet I continue to get an error like this,



And the enemies themselves never spawn. I just end up sitting there the whole game waiting for someone to arrive, but they never do.

Good catch, survival seems to be broken. I'm going to guess it's because that line calls for rte.ShipMassMax, which doesn't exist, so you get an error instead and no ships spawning.
Play skirmish defense or endless skirmish defense instead, I believe they work fine and as far as I know they're essentially the same (do we really need 3 of essentially the same activity?).