I have endured similar ZEN problems to these that you describe. In my case, I concluded that the installation of the ZEN package itself wasn't broken; zen is just cpu intensive. But Zen's setup of my update repository catalog was easily and unpredicatbly damaged. It would work for a few updates, then I'd get undecipherable error messages. That might be what's happened to you.
Here are the gory details
of what I went through getting updating working on my machine. Perhaps it will save you some time debugging your problem.
SUSE 10.2 is my first encounter with ZEN and I don't find much to like. The YaST online updater in 10.0 worked fine and I wish Novell had left it alone.