I'm having weird stuff starting a game as well - instant crashes upon starting the map/world initialisation process - although it seems to be intermittent. It also seems to be when I change map script although that may have been coincidence.
The best thing you can try is starting a 'Normal Game' (not a custom game), accept all the default settings, along with whatever map script you're playing (I'm using ErebusContinents just to make sure I'm at maximum compatibility with whatever Valkrionn's doing).
It may start, it may not.
If it doesn't : Repeat above. You'll probably get it on the second or third try.
Once it starts successfully, then quit and start a Custom Game. Change settings as you prefer (I'd leave Flavour Start in though in particular as the mod semems designed for that) and in my experience you're good to go.
EDIT: It also seems that sometimes the map can get stuck on some kind of 'seed'.
I couldn't generate a map using ErebusContinent for some reason (Crashed on generation over ten times, I was trying some stuff) - so I generated one map with Tectonics which went OK - then went back to ErebusContinent, and generated a map just fine.
Going to be very hard to diagnose, whatever it is
