According to this article in Nature, the reason why the Genesis spacecraft crashed in September was because two switches were installed backwards:

Investigators may have discovered what caused the Genesis spacecraft to crash into the Utah desert this September. Some crucial switches were installed backwards, because of an error in the instructions.

Which of course leads us to today's quote of the day:

"Documentation is like sex: when it is good, it is very, very good; and when it is bad, it is better than nothing."
- Dick Brandon

Unless of course it's just plain wrong.