hhmmm.... so, have you ever tried casting Poison Cloud near somebody, but not directly on them? <img src="/ubbthreads/images/graemlins/badsmile2.gif" alt="" />
The same thing can be done with other area effect spells that do not need a target, as well as the warrior's spin attack, but I found Poison Cloud to work in more cases. Some NPCs are protected and can not be attacked by some/all methods (or they can be attacked, but not killed), and the patch adds protection for more essential NPCs. I'd be careful about killing friendly NPCs until you are sure you no longer need them
<img src="/ubbthreads/images/graemlins/devil.gif" alt="" />