title: Error when launching rails server - getting "uninitialized constant Devise::Models::Invitable (NameError)"
body: <p>I am new to rails and am trying to follow along with this prelaunch signup tutorial - <a href="http://railsapps.github.com/tutorial-rails-prelaunch-signup.html" rel="noreferrer">http://railsapps.github.com/tutorial-rails-prelaunch-signup.html</a></p>
  
  <p>When initializing the rails server using $ rails s, I get the following error message:</p>
  
  <p>Users/pv/.rvm/gems/ruby-1.9.3-p194@rails326/gems/devise-2.1.2/lib/devise/models.rb:97:in `const_get': uninitialized constant Devise::Models::Invitable (NameError)</p>
  
  <p>followed by a bunch of file paths, such as:</p>
  
  <pre><code>from /Users/patrickvihtelic/.rvm/gems/ruby-1.9.3-p194@rails326/gems/devise-2.1.2/lib/devise/models.rb:97:in `block (2 levels) in devise'
  from /Users/patrickvihtelic/.rvm/gems/ruby-1.9.3-p194@rails326/gems/devise-2.1.2/lib/devise/models.rb:92:in `each'
  from /Users/patrickvihtelic/.rvm/gems/ruby-1.9.3-p194@rails326/gems/devise-2.1.2/lib/devise/models.rb:92:in `block in devise'
  from /Users/patrickvihtelic/.rvm/gems/ruby-1.9.3-p194@rails326/gems/devise-2.1.2/lib/devise/models.rb:123:in `devise_modules_hook!'
  from /Users/patrickvihtelic/.rvm/gems/ruby-1.9.3-p194@rails326/gems/devise-2.1.2/lib/devise/models.rb:90:in `devise'
  from /Users/patrickvihtelic/code/rails-prelaunch-signup/app/models/user.rb:5:in `&lt;class:User&gt;'
  from /Users/patrickvihtelic/code/rails-prelaunch-signup/app/models/user.rb:1:in `&lt;top (required)&gt;'
  from /Users/patrickvihtelic/.rvm/gems/ruby-1.9.3-p194@rails326/gems/activesupport-3.2.8/lib/active_support/inflector/methods.rb:230:in `block in constantize'
  from /Users/patrickvihtelic/.rvm/gems/ruby-1.9.3-p194@rails326/gems/activesupport-3.2.8/lib/active_support/inflector/methods.rb:229:in `each'
  from /Users/patrickvihtelic/.rvm/gems/ruby-1.9.3-p194@rails326/gems/activesupport-3.2.8/lib/active_support/inflector/methods.rb:229:in `constantize'
  from /Users/patrickvihtelic/.rvm/gems/ruby-1.9.3-p194@rails326/gems/devise-2.1.2/lib/devise.rb:256:in `get'
  </code></pre>
  
  <p>Can anyone please give me a hint or point me in the right direction?</p>
  
  <p>Thanks!</p>
  
  <p>Pat</p>