The attachment model gets callbacks for removing thumbnails and the actual file:
http://bs.techno-weenie.net/!source/2923/plugins/attachment_fu/lib/technoweenie/attachment_fu.rb#72
So, delete the model and it should clean up the file(s) for you.
That's a problem with your routes or your controller, not attachment_fu. Look at your logs and see why it's a blank screen.
