Hi there. I've been stuck at the same place for days. I've zapped everything that can be zapped (both in the main room and in the kitchen), including the spiders. BUT, the lock will not "activate" (i.e., doesn't respond to a "charged spell). Arrghh! Tried many, many things, but no luck. Starting to wonder if it's a bug....but still assuming I'm missing something....
I'm hoping that some kind soul will give us a pointer! (By the way, I have checked the walkthrough referred to above ("...IGN FAQs"), and have done everything it refers to in this location.)