Form with mulitple records, undefined method `model_name' for Symbol:Class

Question

Rails 3.2 I am getting the an error on the first line at ":photos", it says undefined method 'model_name' of Symbol:Class. Im lost on this one.

= simple_form_for [@tower, :photos], remote: true, html: {class: 'form-horizontal'} do |f|
  = f.error_notification
  .modal-body
    .modal-body-content
      .form-inputs
        - @photos.each_with_index do |photo, index|
          = simple_fields_for photo do |p|
            = render 'form_inputs', f: p, count: index
  .modal-footer
    = f.submit 'Save', class: 'btn btn-primary'
    button.btn type="button" data-dismiss="modal" Cancel

_

# GET /towers/1/photos/new
def new
  @tower = Tower.find(params[:tower_id])
  @photos = Array.new(3){ @tower.photos.build }

  respond_to do |format|
    format.html # new.html.slim
    format.json { render json: @photos }
  end
end

Also in tower.rb "accepts_nested_attributes :photos"