i think there is a bug in nxt.rb:

require "sensors/touch_sensor"
require "sensors/sound_sensor"
require "light_sensor"
require "ultrasonic_sensor"

this should be written as follow:

require "sensors/touch_sensor"
require "sensors/sound_sensor"
require "sensors/light_sensor"
require "sensors/ultrasonic_sensor"

Date: 2009-08-23 21:40
Sender: Daniel Mantilla

I had the same problem and made the change on my local copy.
Are you still using this library to control your NXT? I just
found it today and started playing with it.

Thanks for the tip.

Daniel