I suppose the problem on the first map could be that it is a simple cube with a script that instantly teleports you to the next map upon entering. I think I should add a 1-tic delay or something. It's just a simple trick to have an intermission text before the first real map.
The divide by zero error must be something exclusive for other's computers 'cause mine NEVER had such problem... It's a mistery.
Anyway, just wait for next release to come out... Or try starting the game from the map next to the problematic one.

