"respond_to do |format|" throws UnknownFormat error
<p>I'm trying to render a js file from a controller with ajax. This exact code always worked before, and it even works in other methods, but I suddenly started getting this error:</p>

<pre><code>ActionController::UnknownFormat in MoviesController#vote
ActionController::UnknownFormat
</code></pre>

<p>Movies Controller:</p>

<pre><code>def vote
  ...
  respond_to do |format| #The error points to this line.
    format.js
  end
end
</code></pre>

<p>vote.js.erb:</p>

<pre><code>$('#votes').html("&lt;%= escape_javascript(render 'votes') %&gt;");
</code></pre>

<h2>The link:</h2>

<p>movies.html.erb:</p>

<pre><code>&lt;%= render 'votes' %&gt;
</code></pre>

<p>_votes.html.erb</p>

<pre><code>&lt;%= link_to "vote", vote_path, method: :post, remote: true %&gt;
</code></pre>

<p>routes.rb:</p>

<pre><code>post 'movies/vote' =&gt; 'movies#vote', as: 'vote'
</code></pre>

<p>Why am I suddenly getting this error? Why does it work in different contexts but not in this one?</p>

<p>Using Rails 4.0.10</p>

<h2><strong>UPDATE: Stack Trace</strong></h2>

<p>Application Trace:</p>

<pre><code>app/controllers/movies_controller.rb:394:in `vote'
</code></pre>

<p>Full Trace:</p>

<pre><code>actionpack (4.0.10) lib/action_controller/metal/mime_responds.rb:372:in `retrieve_collector_from_mimes'
actionpack (4.0.10) lib/action_controller/metal/mime_responds.rb:189:in `respond_to'
app/controllers/movies_controller.rb:394:in `vote'
actionpack (4.0.10) lib/action_controller/metal/implicit_render.rb:4:in `send_action'
actionpack (4.0.10) lib/abstract_controller/base.rb:189:in `process_action'
actionpack (4.0.10) lib/action_controller/metal/rendering.rb:10:in `process_action'
actionpack (4.0.10) lib/abstract_controller/callbacks.rb:18:in `block in process_action'
activesupport (4.0.10) lib/active_support/callbacks.rb:413:in `_run__1492335060096380544__process_action__callbacks'
activesupport (4.0.10) lib/active_support/callbacks.rb:80:in `run_callbacks'
actionpack (4.0.10) lib/abstract_controller/callbacks.rb:17:in `process_action'
actionpack (4.0.10) lib/action_controller/metal/rescue.rb:29:in `process_action'
actionpack (4.0.10) lib/action_controller/metal/instrumentation.rb:31:in `block in process_action'
activesupport (4.0.10) lib/active_support/notifications.rb:159:in `block in instrument'
activesupport (4.0.10) lib/active_support/notifications/instrumenter.rb:20:in `instrument'
activesupport (4.0.10) lib/active_support/notifications.rb:159:in `instrument'
actionpack (4.0.10) lib/action_controller/metal/instrumentation.rb:30:in `process_action'
actionpack (4.0.10) lib/action_controller/metal/params_wrapper.rb:250:in `process_action'
activerecord (4.0.10) lib/active_record/railties/controller_runtime.rb:18:in `process_action'
actionpack (4.0.10) lib/abstract_controller/base.rb:136:in `process'
actionpack (4.0.10) lib/abstract_controller/rendering.rb:44:in `process'
actionpack (4.0.10) lib/action_controller/metal.rb:195:in `dispatch'
actionpack (4.0.10) lib/action_controller/metal/rack_delegation.rb:13:in `dispatch'
actionpack (4.0.10) lib/action_controller/metal.rb:231:in `block in action'
actionpack (4.0.10) lib/action_dispatch/routing/route_set.rb:82:in `call'
actionpack (4.0.10) lib/action_dispatch/routing/route_set.rb:82:in `dispatch'
actionpack (4.0.10) lib/action_dispatch/routing/route_set.rb:50:in `call'
actionpack (4.0.10) lib/action_dispatch/journey/router.rb:71:in `block in call'
actionpack (4.0.10) lib/action_dispatch/journey/router.rb:59:in `each'
actionpack (4.0.10) lib/action_dispatch/journey/router.rb:59:in `call'
actionpack (4.0.10) lib/action_dispatch/routing/route_set.rb:676:in `call'
warden (1.2.3) lib/warden/manager.rb:35:in `block in call'
warden (1.2.3) lib/warden/manager.rb:34:in `catch'
warden (1.2.3) lib/warden/manager.rb:34:in `call'
rack (1.5.5) lib/rack/etag.rb:23:in `call'
rack (1.5.5) lib/rack/conditionalget.rb:25:in `call'
rack (1.5.5) lib/rack/head.rb:11:in `call'
actionpack (4.0.10) lib/action_dispatch/middleware/params_parser.rb:27:in `call'
actionpack (4.0.10) lib/action_dispatch/middleware/flash.rb:241:in `call'
rack (1.5.5) lib/rack/session/abstract/id.rb:225:in `context'
rack (1.5.5) lib/rack/session/abstract/id.rb:220:in `call'
actionpack (4.0.10) lib/action_dispatch/middleware/cookies.rb:486:in `call'
activerecord (4.0.10) lib/active_record/query_cache.rb:36:in `call'
activerecord (4.0.10) lib/active_record/connection_adapters/abstract/connection_pool.rb:626:in `call'
activerecord (4.0.10) lib/active_record/migration.rb:373:in `call'
actionpack (4.0.10) lib/action_dispatch/middleware/callbacks.rb:29:in `block in call'
activesupport (4.0.10) lib/active_support/callbacks.rb:373:in `_run__2656547782179467807__call__callbacks'
activesupport (4.0.10) lib/active_support/callbacks.rb:80:in `run_callbacks'
actionpack (4.0.10) lib/action_dispatch/middleware/callbacks.rb:27:in `call'
actionpack (4.0.10) lib/action_dispatch/middleware/reloader.rb:64:in `call'
actionpack (4.0.10) lib/action_dispatch/middleware/remote_ip.rb:76:in `call'
actionpack (4.0.10) lib/action_dispatch/middleware/debug_exceptions.rb:17:in `call'
web-console (2.2.1) lib/web_console/middleware.rb:39:in `call'
actionpack (4.0.10) lib/action_dispatch/middleware/show_exceptions.rb:30:in `call'
railties (4.0.10) lib/rails/rack/logger.rb:38:in `call_app'
railties (4.0.10) lib/rails/rack/logger.rb:20:in `block in call'
activesupport (4.0.10) lib/active_support/tagged_logging.rb:68:in `block in tagged'
activesupport (4.0.10) lib/active_support/tagged_logging.rb:26:in `tagged'
activesupport (4.0.10) lib/active_support/tagged_logging.rb:68:in `tagged'
railties (4.0.10) lib/rails/rack/logger.rb:20:in `call'
actionpack (4.0.10) lib/action_dispatch/middleware/request_id.rb:21:in `call'
rack (1.5.5) lib/rack/methodoverride.rb:21:in `call'
rack (1.5.5) lib/rack/runtime.rb:17:in `call'
activesupport (4.0.10) lib/active_support/cache/strategy/local_cache.rb:83:in `call'
rack (1.5.5) lib/rack/lock.rb:17:in `call'
actionpack (4.0.10) lib/action_dispatch/middleware/static.rb:64:in `call'
rack (1.5.5) lib/rack/sendfile.rb:112:in `call'
railties (4.0.10) lib/rails/engine.rb:511:in `call'
railties (4.0.10) lib/rails/application.rb:97:in `call'
rack (1.5.5) lib/rack/lock.rb:17:in `call'
rack (1.5.5) lib/rack/content_length.rb:14:in `call'
rack (1.5.5) lib/rack/handler/webrick.rb:60:in `service'
/home/greg/.rvm/rubies/ruby-2.0.0-p648/lib/ruby/2.0.0/webrick/httpserver.rb:138:in `service'
/home/greg/.rvm/rubies/ruby-2.0.0-p648/lib/ruby/2.0.0/webrick/httpserver.rb:94:in `run'
/home/greg/.rvm/rubies/ruby-2.0.0-p648/lib/ruby/2.0.0/webrick/server.rb:295:in `block in start_thread'
</code></pre>