title: carrierwave thumb issue
body: <p>This question was asked, but no answer given...I'm having the same issue. </p>
  
  <p>I'm using carrierwave for uploading files everything works great until i wanted to create thumbs</p>
  
  <p>images are saved in a tmp direct, but kept at the same size...</p>
  
  <p>My avatar_uploader.rb file looks like this:</p>
  
  <pre><code>class AvatarUploader &lt; CarrierWave::Uploader::Base
  include CarrierWave::RMagick
  storage :file
  def store_dir
     "uploads/#{model.class.to_s.underscore}/#{mounted_as}/#{model.id}"
  end
  version :thumb do
    process :resize_to_limit =&gt; [200, 200]
  end
  </code></pre>
  
  <p>My view has the following:</p>
  
  <pre><code>&lt;% for image in @posts %&gt;
  &lt;%= image_tag image.avatar_url(:thumb) if image.avatar? %&gt;
  &lt;%= image.title %&gt;
  &lt;% end %&gt;
  </code></pre>
  
  <p>When I don't include (:thumb), I see the full images...but when I do include the (:thumb), I get the following error:</p>
  
  <pre><code>Version thumb doesn't exist!
  </code></pre>
  
  <p>below is my model setup</p>
  
  <pre><code>class Post &lt; ActiveRecord::Base
    attr_accessible :comments, :frame, :title, :twitter, :avatar
    belongs_to :user
    mount_uploader :avatar, AvatarUploader
  end
  </code></pre>
  
  <p>I can see that a tmp directory was created, but images not resized...I have imagemagick and rmagick installed...</p>
  
  <p>Thank you</p>