Rails 4.2.3 Active Admin error

Im on Windows 7 running Rails 4.2.3 and I have been trying to install active admin as part of an older tutorial.

I updated my Gemfile

# Bundle edge Rails instead: gem 'rails', github: 'rails/rails'
gem 'rails', '4.2.3'
# Use sqlite3 as the database for Active Record
#gem 'sqlite3'


gem 'pg'
gem 'activeadmin', github: 'activeadmin'

# Use SCSS for stylesheets
gem 'sass-rails', '~> 5.0'
# Use Uglifier as compressor for JavaScript assets
gem 'uglifier', '>= 1.3.0'
# Use CoffeeScript for .coffee assets and views
gem 'coffee-rails', '~> 4.1.0'
# See http://ift.tt/1D4cmMg for more supported runtimes
# gem 'therubyracer', platforms: :ruby

# Use jquery as the JavaScript library
gem 'jquery-rails' 

.........etc

Ran

$bundle install

then

$rails g active_admin:install --skip-users

$ rake db:migrate

restarted my server going to localhost:3000/admin throws this error:

ExecJS::ProgramError in Admin::Dashboard#index

Showing C:/Ruby21-x64/lib/ruby/gems/2.1.0/bundler/gems/activeadmin-3254f53b4b35/app/views/active_admin/page/index.html.arb where line #2 raised:

TypeError: Object doesn't support this property or method

//

I feel like i've followed all the documents on how to install this and have run out of things to read. Is there just some beginner's error here or am I missing something?

as requested here is the code from the index.html.arb file for the gem which is only one line....

insert_tag active_admin_application.view_factory["page"]

via Chebli Mohamed