Processing HostsController#medium_selected (for 10.35.1.213 at 2011-08-07 14:35:07) [POST]
  Parameters: {"action"=>"medium_selected", "authenticity_token"=>"/viBXhzUogK80sH32jnr9MR4yMNKR8uUqRkKdvALl5w=", "controller"=>"hosts", "host"=>{"architecture_id"=>"1", "use_image"=>"undefined", "medium_id"=>"3", "operatingsystem_id"=>"16"}}

ActionView::TemplateError (undefined method `file_prefix' for #<ActiveRecord::Associations::BelongsToAssociation:0x7f8b22b87180>) on line #8 of app/views/common/os_selection/_image_details.html.erb:
5:     <%= check_box_tag type + "[use_image]", 1, item.use_image, :id => type + "_cb_use_image" -%>
6:   </span>
7:   <%= label_tag "#{item}_image_file", "Image filename",  :class => "span-4" -%>
8:   <%= image_file_entry item-%>
9:   <%= observe_field type + "_cb_use_image",
10:     :url => { :action => :use_image_selected },
11:     :with => "'#{type}[use_image]=' + value + '&#{type}[medium_id]=' + $('##{type}_medium_id').val() + '&#{type}[operatingsystem_id]=' + $('##{type}_operatingsystem_id').val() + '&#{type}[architecture_id]=' + $('##{type}_architecture_id').val() + '&#{type}[model_id]=' + $('##{type}_model_id').val()"