routing issue with mounted engine - Rails 3.2.8

I mounted the Forem::Engine in my app

MyApp::Application.routes.draw do     scope "/:locale" do     ...     resources :sites, :only => [:none] do       get 'home', :on => :collection       get 'events', :on => :collection    end     ..     mount Forem::Engine, :at => "/forums", :as => :forums, constraints: lambda { |r| r.subdomain.present? && r.subdomain != 'www' } , :defaults => { :locale => I18n.locale }    ...   end

when I display the home page of the subdomain, http://bingo.lvh.me:3000/ I don't have any problem with the navbar links in the header in which I have : = link_to t(:home), home_sites_path(:locale => I18n.locale) = link_to t(:forums), forums_path(:locale => I18n.locale)

Upon clicking on 'forums' item ( generated url: bingo.lvh.me:3000/ en/forums ) , I am redirected correctly to the engine Forem::forums#index, the rendering raises an error with the home link ...

undefined method `home_sites_path' for #<#<Class:0x007fdd936ce5f8>: 0x007fdd96db7e70> it seems that my app routing is lost

despite the fact that I get the route in my routes.rb, but maybe 'forums_path' is not the right

what could be wrong ? thanks for feedback