Don't install it globally. Only install modules globally which you'll be using command line interfaces of, like mocha or casper. Anything you "require" in your app is installed locally.
I can't think of any reason it shouldn't be working in that case :/. Try deleting the folder, clearing npm cache (npm cache clean) and installing it again. Also, are the other modules working fine?
require" in your app is installed locally.npm cache clean) and installing it again. Also, are the other modules working fine?require()line you use to load it.