title: Mass assignment failure in Nested form
body: <p>I'm facing a common problem that novices face with Rails 3.2.3. I am getting error </p>
  
  <p>Can't mass-assign protected attributes: user_impl, util_location</p>
  
  <pre><code>class User &lt; ActiveRecord::Base
  
    has_one :user_impl, :dependent =&gt; :destroy
    has_one :util_location, :as =&gt; :locatable, :dependent =&gt; :destroy
  
    attr_accessible ..., :user_impl_attributes, :util_location_attributes
  </code></pre>
  
  <p>I tried adding accepts_nested_attributes_for :user_impl, :util_location to the code too but that too is not working and giving an altogether different error.</p>