NotImplementedError when switching to Poltergeist

I have this cucumber step definitions that work with Selenium but I get `NotImplementedError` when I try them with the poltergeist driver. phantom.js is installed and I can even take screenshots from my step definitions that look right. I'm testing an Ember.js/Rails application. See that it visits the page correctly but then it fails when I try to find a link. ``` When(/^I visit the App$/) do visit("/") end Then(/^I should see link "(.*?)"$/) do |arg1| find_link(arg1) end When(/^I click "(.*?)"$/) do |arg1| find_link(arg1).click end When(/^I fill in "(.*?)" with "(.*?)"$/) do |arg1, arg2| fill_in arg1, :with => arg2 end When(/^I click "(.*?)" button$/) do |arg1| find_button(arg1).click end ``` The exact error is this: ``` When I visit the App # features/step_definitions/sign_in_steps.rb:1 Then I should see link "Sign Up" # features/step_definitions/sign_in_steps.rb:5 NotImplementedError (NotImplementedError) ./features/step_definitions/sign_in_steps.rb:6:in `/^I should see link "(.*?)"$/' features/sign_in.feature:9:in `Then I should see link "Sign Up"' ```