acts_as_list error - help!

I'm having a problem with acts_as_list, and I'm stumped. I have two models: page and item. A page contains a list of items:

class Page < ActiveRecord::Base   has_many :items, :dependent => :destroy, :order => :position   belongs_to :portfolio ...

class Item < ActiveRecord::Base   belongs_to :page   acts_as_list :scope => :page ...

When I try to destroy an item, I get this error:

NoMethodError in ItemsController#destroy undefined method `updated?' for #<Page:0x26eeedc>

If I remove the :dependent => :destroy in the has_many declaration, everything works fine (the item's page_id is nulled, but the item isn't destroyed). Any idea what I'm doing wrong? I've Googled til my fingers bled, but no luck. Any help is greatly appreciated!