attachmet fu thumbs not generated

Hi all,

I use attachment fu for image upload. In my model I define 3 thumbs.
The orginal image is resized but the thumbnails are not. People have
reported this issue before but I have not seen a solution yet.

I have this issue both on Windows and Linux.

Someonehas a solution for this?
thanks
Stijn

class Image < ActiveRecord::Base
  belongs_to :album
  has_attachment :content_type => :image,
                 :storage => :file_system,
                 :max_size => 500.kilobytes,
                 :resize_to => '384x256>',
                 :thumbnails => {
                   :large => '96x96>',
                   :medium => '64x64>',
                   :small => '48x48>'
                 }

  validates_as_attachment
end