There used to be a bug where when you jumped down, and the game switched to the next map, you\'d start standing on a transparent floor then as soon as you moved you\'d fall and die. Switching load all maps on fixed it. so that you jumped right down in one go and were okay.
However, I think that\'s fixed now - certainly works on my system without turning on load all maps.
Maybe you character\'s just not strong enough to survive the fall.