problem with Rails 2 and XML Builder

I get the following error after converting to Rails 2 when trying to serve an XML file (xml.builder file)

ActionController::MissingTemplate (Missing template chart/ refresh_activity_data.html.erb in view path /Users/madhukarpadma/ Desktop/halo2.0/app/views): /vendor/rails/actionpack/lib/action_controller/base.rb:1269:in `assert_existence_of_template_file'

The view is an XML builder file called refresh_activity_data.xml.builder

The code in the chart_controller is render :template => 'chart/refresh_activity_data', :layout => false

What do we change this last line to exactly to get the xml.builder file?