Rails plugin with only assets

backbone-bundle.gemspec

$:.push File.expand_path("../lib", __FILE__)

# Maintain your gem's version:
require "backbone-bundle/version"

# Describe your gem and declare its dependencies:
Gem::Specification.new do |s|
  s.name        = "backbone-bundle"
  s.version     = BackboneBundle::VERSION
  s.authors     = ["Prevole"]
  s.email       = ["realemailthere"]
  s.homepage    = "someurlthere"
  s.summary     = "Toolbox of different piece of backbone codes."
  s.description = "Contains the different useful javascript files for backbone."

  s.files = Dir["{lib,vendor}/**/*"]
  s.files.reject! { |fn| fn.include? "lib/tasks" } 
  s.test_files = Dir["test/**/*"]
  s.require_paths = ["lib"]

  s.add_dependency "rails", "~> 3.2.6"
end

libbackbone-bundle.rb

require "backbone-bundle/version"
require "backbone-bundle/engine"

libbackbone-bundleengine.rb

module BackboneBundle
  class Engine < ::Rails::Engine
  end
end

libbackbone-bundleversion.rb

module BackboneBundle
  VERSION = "0.0.1"
end

otherproject-app-assets-javascripts-application.coffee

#= require backbone # Working
#= require backbone.layoutmanager # Not working, Error: the file is not found

otherproject-Gemfile

# ...
group :assets do
  gem 'sass-rails', '~> 3.2.3'
  gem 'backbone-on-rails'
  gem 'backbone-bundle'
  gem 'haml_coffee_assets'
  gem 'execjs'
  gem 'i18n-js'
end
# ...

vendor-assets-javascripts-backone.layoutmanager.js

// The javascript code of backbone/layoutmanager extension that is probably not relevant for my problem

The real error I got when I try to access any page that require application.coffee/js in my main project:

Sprockets::FileNotFound in …

couldn't find file 'backbone.layoutmanager'

Thans to Radar on the #rubyonrails. The solution was really simple. Just restarted the rails server and it worked. Newbie error.