Game froze while building. That's not good!
edit: Make that twice in a row. Looks like I won't be repeating that step again...
edit 2: Okay, now my level won't load (as in, it's stuck on a loading screen after a few minutes of letting it run, to the point where loading sounds aren't coming from my system anymore). Although I think this has happened once before and I was able to get through in the end, I'm still VERY scared.