I don't think NC works well with the "free" gij Java implementation that comes with Ubuntu by default. You should install Sun's Java instead. Use Synaptic to search for sun-java6-jre and install it, or else from the command line use:
Code:
sudo aptitude install sun-java6-jre
(enter your password when asked). Hopefully when you do this it will become the default Java install. If you continue to get the same error, post and I'll tell you have to change the default using the "alternatives" feature of the system.