Cloud 9 & Rails: Cannot GET /dev_focus/focus/rails/mailers/user_mailer/account_activation

I am following through with the Rails Tutorial by Michael Hartl but have come to a bump in the road when trying to preview my mailers using the Cloud 9 IDE.

Here is my user_mailer.rb

class UserMailer < ApplicationMailer

def account_activation(user)
   @user=user
   mail to: user.email, subject: "Activate your focus. account"
end

def password_reset
  @greeting = "Hi"

  mail to: "to@example.org"
end
end

My problem is when I attempt to preview my mailers using the link

http://http://ift.tt/1oINnud/rails/mailers/user_mailer/account_activation

I get a blank page with the following error:

Cannot GET /dev_focus/focus/rails/mailers/user_mailer/account_activation

Any Ideas?

Thanks for your help!