format.atom w Rails 2.2

in Rails 2.1, this works.. but I am stuck w Rails 2.2

class PostsController < ApplicationController
  def show
     ......
    respond_to do |format|
      format.html
      format.atom { render :action => 'changes', :layout =>
false, :content_type => 'application/atom+xml' }
    end
  end

  def changes
     ........
    respond_to do |format|
      format.xml { render :layout => false, :content_type =>
'application/atom+xml' }
    end
  end
..
end

I have a view, changes.xml.builder, building the xml code, but I got
a missing template as an error, when executing
http://localhost:3000/posts/show/5

ActionView::MissingTemplate (Missing template posts/changes.erb in
view path .../Projects/franchising/app/views:):
If I set a changes.erb, the xml code is sent...

how should I write that w Rails 2.2 ?

thanks a lot for your help

erwin

mistaken.... shoudl write changes.rxml and not xml.builder !!!
dawned copy/paste !!