I seem to be a little ignorant about linking node groups. When I try to use node groups from other files in a project I'm working on, for some reason in the materials preview box the material shows up as black instead of what it should be (in this case a shiny metal). The group has obviously been set up correctly since it worked in its native file, but when I try to use it in my project after linking the two it doesn't show up correctly.
If there's anything I can offer to help solve this problem then please tell me what to do, but I hope this is simple enough that someone with more knowledge will know exactly what the problem is.
Here is the .blend file : http://www.pasteall.org/blend/31640