Hieraki help

I need to set up a Wiki for a project that I'm working on, and HIeraki seems to be the best rails-based option for my needs. I've got it installed & with the help of some notes on the net, it's mostly working. Unfortunately there are a few big bugs still, including one when I try to create a new page. I'm new enough at Rails that my debugging skills are seriously lacking. Can anyone offer any suggestions? The relevant code is below the error message.

Any help is appreciated! Thanks, Mike