Carrierwave + Fog (S3) + Heroku: TypeError (can't convert Hash into String)

I have an application on Heroku that uses Carrierwave to upload images to S3. The app is running perfectly on local machine but on Heroku throws the following error and fails the uploading to S3:

TypeError (can't convert Hash into String):
2011-09-23T15:12:07+00:00 app[web.1]:   app/controllers/admin/albums_controller.rb:49:in `create'
2011-09-23T15:12:07+00:00 app[web.1]:   app/controllers/admin/albums_controller.rb:48:in `create'

That line corresponds to the "if @album.save" instruction.

My Albums controller create action is:

def create
@album = Album.new(params[:album])

respond_to do |format|
  if @album.save
    format.html { redirect_to(admin_album_path(@album), :notice => 'Àlbum creat correctament.') }
    format.xml  { render :xml => [:admin, @album], :status => :created, :location => @album }
  else
    format.html { render :action => "new" }
    format.xml  { render :xml => @album.errors, :status => :unprocessable_entity }
  end
end
end

My Carrierwave initializer:

CarrierWave.configure do |config|
    config.fog_credentials = {
      :provider               => 'AWS', 
      :aws_access_key_id      => APP_CONFIG['storage']['s3_access'],
      :aws_secret_access_key  => APP_CONFIG['storage']['s3_secret'],
    }
    config.fog_directory  = 'romeu'
    config.fog_host       = 'http://xxxxx.s3.amazonaws.com'
    config.fog_public     = true
    config.root = Rails.root.join('tmp')
    config.cache_dir = 'carrierwave'
end

My image_uploader.rb:

class ImageUploader < CarrierWave::Uploader::Base

include CarrierWave::MiniMagick

storage :fog

def store_dir
  "uploads/#{model.class.to_s.underscore}/#{mounted_as}/#{model.id}"
end

# Album Cover version
version :cover do
  process :square_resize => [150,150]
end

# Thumb version
version :thumb do
  process :square_crop => [80,80]
end

def square_crop(width, height)
  manipulate! do |img|
    side = [img['width'], img['height']].min
    x = (img['width'] - side) / 2
    y = (img['height'] - side) / 2
    img.crop("#{side}x#{side}+#{x}+#{y}")
    img.resize("#{width}x#{height}")
    img
  end
end

def square_resize(width, height)
  manipulate! do |img|
    img.resize("#{width}x#{height}")
    img
  end
end

# Valid list
def extension_white_list
    %w(jpg jpeg gif png)
end
end

My config.ru:

# This file is used by Rack-based servers to start the application.

require ::File.expand_path('../config/environment',  __FILE__)
use Rack::Static, :urls => ['/carrierwave'], :root => 'tmp'
run Encen::Application

I have inspected the @album object and everything seems okay:

_mounters: 
  :image: !ruby/object:CarrierWave::Mount::Mounter 
    _memoized_option: 
      ? 
        - :mount_on
      : 

    column: :image
    integrity_error: 
    options: {}

    processing_error: 
    record: *id001
    uploader: !ruby/object:ImageUploader 
      cache_id: 20110923-0810-1-0644
      file: !ruby/object:CarrierWave::SanitizedFile 
        content_type: image/jpeg
        file: /app/tmp/carrierwave/20110923-0810-1-0644/image.jpg
        original_filename: 
      filename: image.jpg
      model: *id001
      mounted_as: :image
      original_filename: image.jpg
      versions: 
        :thumb: !ruby/object: 
          file: !ruby/object:CarrierWave::SanitizedFile 
          cach开发者_如何学JAVAe_id: 20110923-0810-1-0644
            content_type: image/jpeg
            file: /app/tmp/carrierwave/20110923-0810-1-0644/image.jpg
            original_filename: 
          filename: image.jpg
          model: *id001
          mounted_as: :image
          original_filename: image.jpg
          parent_cache_id: 20110923-0810-1-0644
          versions: {}

        :cover: !ruby/object: 
          cache_id: 20110923-0810-1-0644
          file: !ruby/object:CarrierWave::SanitizedFile 
            content_type: image/jpeg
            file: /app/tmp/carrierwave/20110923-0810-1-0644/image.jpg
            original_filename: 
          filename: image.jpg
          model: *id001
          mounted_as: :image

attributes: 

  title: 
  body: 
    model: *id001
previously_changed: {}
readonly: false

I have spent a bunch of days intending to resolve that error but unsuccessful, what I am missing? Thanks in advance.

After long days of frustation I have solved the problem. It was such as an stupid thing like the environment vars of S3 access keys on Heroku were incorrectly defined. I don't understand why Fog gem don't gives you more accurate debugging information about that kind of errors.