http://www.sendspace.com/file/saptsv
It's not even close to being finished. There is no sign and no exit sector, no thok barrier (yet; I'm making it up as I go so I don't know how big the barrier should be, so I plan on putting it in when I'm done) and the beach has a ton of issues (like an invisible wall preventing you from getting in, the wall being closer to the water than it should be, etc.). To get to where it crashes, from the start turn around and roll through the wall with vines on it. Bounce up the springs, jump over the death pit, and run down there until you hit the invisible wall (still trying to figure that out, might eventually need help with that). Walk to the left and turn the camera until you can see through the left wall (since the thok barrier's not in place) and you should see the cavern out there. Right around there the game crashes. It might crash here because the thok barrier's not in place, but that cavern is already accessable and being underwater in the wrong spot there might cause the same error. Earlier in the level's development I had the route behind the wall merging with a route underwater in the cavern, but the game crashed. I gave the route behind the wall its own path to the beach, and the game stopped crashing there, but crashed when you got to the beach. Took out the underwater passage and the game stopped crashing when you get to the beach, but it's still screwed up if you can see where the underwater passage used to be. Putting in the thok barrier might stop it, but I'd really like to know why this passage is crashing the game and how I can prevent it with future paths.
EDIT: Wow, I'm stupid. I think I figured it out. I accidentally forgot to remove a spring and a checkpoint that used to be in the passage. The game probably crashes because it doesn't know where to put them, since the sector and linedefs are gone. Still, I'd like to know why the game crashed when the passage was still there.
EDIT: For some reason I can't turn the camera through the left wall anymore.
Anyway, new crash. From the start, go straight. Jump up the platforms and on to the spring and into the cave. Go a bit farther and you'll get into the cavern. There is one wall that apparently has no textures on it (need to fix that). This wall is where the underwater passage used to be; walk up to it and turn the camera until it crashes.
Apparently the checkpoint and spring weren't the only reasons the game crashed. Also, the game crashes if you put the camera through the wall on the left as you're jumping up the springs.
I know putting in the thok barrier might prevent these, but I don't know if it can crash without putting the camera outside the level and I'd like to find out why this underwater passage is screwing up the level, even though I deleted it.