Can't Dump file - paperclip with workling and starling

here is my controller action:

def create
   UploadWorker.async_send_file(params[:image])

flash[:notice] = "uploading file"
redirect_to root_url
end

class UploadWorker < Workling::Base
  def send_file(options)
     @image = current_user.images.build(params[:image])
     @image.save
  end
end

I would like the paperclip upload, conversion and save to take place in
the background.
The error I get:

can't dump File

/usr/lib/ruby/gems/1.8/gems/memcache-client-1.8.5/lib/memcache.rb:360:in
`dump'
/usr/lib/ruby/gems/1.8/gems/memcache-client-1.8.5/lib/memcache.rb:360:in
`set_without_newrelic_trace'
(eval):5:in `set'
(eval):4:in `set'
app/controllers/images_controller.rb:52:in `create'

{"commit"=>"upload",
"authenticity_token"=>"3JniM+vyc29t+23lnQjm0RNjrzV37YswhK/fauMfEZY=",
"image"=>{"photo"=>#<File:/tmp/RackMultipart20100814-12328-bwjqb8-0>,
"location"=>"",
"uid"=>"upload_workers:send_file:37ec9541ff9c36d5a7ac802822316d77",
"description"=>"",
"state_id"=>"1"}}