Reason for Errors

delayed_job.rb

       def enqueue(*args)
          object = args.shift
          unless object.respond_to?(:perform)
            raise ArgumentError, 'Cannot enqueue items which do not respond to perform'
          end 
        
          priority = args.first || Delayed::Worker.default_priority
          run_at   = args[1]
          self.create(:payload_object => object, :priority => priority.to_i, :run_at => run_at)
        end 

# Delayed::Job.enqueue takes the first argument as the object, and expects the second object to be a priority int-able, not a hash

delayed_paperclip.rb

       define_method "enqueue_job_for_#{name}" do
          return unless self.send("#{name}_changed?")

          # Paperclip::Attachment#queue_existing_for_delete sets paperclip
          # attributes to nil when the record has been marked for deletion
          return if self.class::PAPERCLIP_ATTRIBUTES.map { |suff| self.send "#{name}#{suff}" }.compact.empty?

          if delayed_job?
            Delayed::Job.enqueue(DelayedPaperclipJob.new(self.class.name, read_attribute(:id), name.to_sym), :priority => priority)
          elsif resque?
            Resque.enqueue(ResquePaperclipJob, self.class.name, read_attribute(:id), name.to_sym)
          end
        end

# Delayed::Job.enqueue is called with the object passed in as arg[0], and {:priority => 0} as arg[1]

suggested_fix.txt

Suggested steps:

   - Modify delayed_paperclip/lib/delayed/paperclip.rb:31 to read:
     Delayed::Job.enqueue(DelayedPaperclipJob.new(self.class.name, read_attribute(:id), name.to_sym), priority)

     (This has been hotfixed in production, and the Study.download_pdf! method passed)

   - There is no versioning set up on delayed_paperclip (or indeed on many of these gems). Issue could resurface on subsequent deploys - this should be frozen.