Any particular values? I see that using "extreme" values (e.g. 1) can sometimes either cause the RTP to go black and not recover (even if normal values are re-entered), or crash (especially in the case of really extreme values like 1). Were you using weird/crazy/extreme values, or more normal ones? The sliders keep you to normal values, which might explain why it doesn't crash in that case.
If you're using strange values then try doing it with the regular preview (not RTP), and you may get "ray trace errors" of some kind, which would help explain and diagnose what's going on. If you don't get those errors with the regular preview and the RTP still crashes with the same value(s) entered that would be interesting, we haven't been able to duplicate that yet.
- Oshyan