Sorry, I didn't see your post until today...

You didn't indicate which version of Zen Cart you're using, but you need to make sure that you're using the version of the Notifier Trace that matches your installed version. Make sure that your class definition looks similar to:

Code:
class un_wishlist extends base {
  Your code here ...
}
Another add-on that I've found useful in debugging classes is Super Globals Plus. Don't be put off by its release date (2007); I'm using it on two v1.3.9 sites with no problems.