Help-me please. Error on include attachment

[Alex Ferreira]

Eu estou tentando Utilizar o lipsiadmin com o attachment porém estou
encontrando o seguinte erro no console quando tento incluir uma
imagem.

my model:
class Line < ActiveRecord::Base
has_many :products
has_friendly_id :titulo, :use_slug => true, :approximate_ascii =>
true

has_one_attachment :imagem_linha, :dependent => :destroy
end


my form:
=simple_error_messages_for :line
-tab :general do
%table.full
%tr
%td.fixed=human_name_for :line, :titulo
%td=text_field :line, :titulo
%tr
%td.fixed=human_name_for :line, :descricao
%td=text_area :line, :descricao
%tr
%td.fixed=human_name_for :line, :imagem_linha
%td=attachment_tag(:line, :imagem_linha, :image => true, :order
=> true)
%tr
%td.fixed=human_name_for :line, :status
%td=check_box :line, :status

error returned in the console

[Attachment] Attachment on Attachment initialized.

ActiveRecord::ReadOnlyRecord (ActiveRecord::ReadOnlyRecord):
app/controllers/backend/lines_controller.rb:43:in `update'
haml (3.0.15) lib/sass/plugin/rack.rb:41:in `call'
/usr/local/rvm/rubies/ruby-1.8.7-p299/lib/ruby/1.8/webrick/
httpserver.rb:104:in `service'
/usr/local/rvm/rubies/ruby-1.8.7-p299/lib/ruby/1.8/webrick/
httpserver.rb:65:in `run'
/usr/local/rvm/rubies/ruby-1.8.7-p299/lib/ruby/1.8/webrick/server.rb:
173:in `start_thread'
/usr/local/rvm/rubies/ruby-1.8.7-p299/lib/ruby/1.8/webrick/server.rb:
162:in `start'
/usr/local/rvm/rubies/ruby-1.8.7-p299/lib/ruby/1.8/webrick/server.rb:
162:in `start_thread'
/usr/local/rvm/rubies/ruby-1.8.7-p299/lib/ruby/1.8/webrick/server.rb:
95:in `start'
/usr/local/rvm/rubies/ruby-1.8.7-p299/lib/ruby/1.8/webrick/server.rb:
92:in `each'
/usr/local/rvm/rubies/ruby-1.8.7-p299/lib/ruby/1.8/webrick/server.rb:
92:in `start'
/usr/local/rvm/rubies/ruby-1.8.7-p299/lib/ruby/1.8/webrick/server.rb:
23:in `start'
/usr/local/rvm/rubies/ruby-1.8.7-p299/lib/ruby/1.8/webrick/server.rb:
82:in `start'