First two possible issues that come to mind.
Does everyone have the exact same map? DK2 is extremely picky about this.
It's possible that the error is simply caused by having a computer in Player 2 position, and then having a Human Player 2 in Player 3 position and so on. Have you tried no computers at all?
I can look into the map further but that'll take some time, I'm not sure if I can get around to it today.