Yutaka,
I am beginning to think that most of the hang-up problems are due to the screen-saver.  NT-4 seems to want a lot of memory (RAM) for this and this could be causing the problem.  Since we did not run the screen saver on the test machine here and it did not crash, I suggest you disable the NTT screen-saver.  This is also something you could try on the NIED s/v controller.
Rod Larson
