PDF attachment broken on rails 3.1.6 production environment - ruby-on-rails

Question

I store a pdf document in the database and send it by email with this lines of code:+
def invoice(payment)
#payment = payment
#user = payment.subscriber or raise(ActiveRecord::RecordNotFound)
#subscription = payment.subscription or raise(ActiveRecord::RecordNotFound)
attachments[#payment.invoice_doc_name] = {
:mime_type => 'application/pdf',
:encoding => 'base64',
:content => #payment.invoice_pdf
}
mail to: #user.email
end
This works perfectly fine on my dev, test and staging environment which is on Heroku Cedar like production. The PDF is correct, I can download it in the user interface. Production configuration is:
Railsapp::Application.configure do
# Settings specified here will take precedence over those in config/application.rb
# Code is not reloaded between requests
config.cache_classes = true
# Full error reports are disabled and caching is turned on
config.consider_all_requests_local = false
config.action_controller.perform_caching = true
# Disable Rails's static asset server (Apache or nginx will already do this)
config.serve_static_assets = true
# Compress JavaScripts and CSS
config.assets.compress = true
# Specify the default JavaScript compressor
config.assets.js_compressor = :uglifier
# Specifies the header that your server uses for sending files
# (comment out if your front-end server doesn't support this)
config.action_dispatch.x_sendfile_header = nil
# Force all access to the app over SSL, use Strict-Transport-Security, and use secure cookies.
config.force_ssl = true
# See everything in the log (default is :info)
# config.log_level = :debug
# Use a different logger for distributed setups
config.logger = Logger.new($stdout)
# Use a different cache store in production
# config.cache_store = :mem_cache_store
# Enable serving of images, stylesheets, and JavaScripts from an asset server
# config.action_controller.asset_host = "http://assets.example.com"
# Precompile additional assets (application.js, application.css, and all non-JS/CSS are already added)
# config.assets.precompile += %w( search.js )
# Disable delivery errors, bad email addresses will be ignored
# config.action_mailer.raise_delivery_errors = false
# Enable threaded mode
# config.threadsafe!
# Enable locale fallbacks for I18n (makes lookups for any locale fall back to
# the I18n.default_locale when a translation can not be found)
config.i18n.fallbacks = true
# Send deprecation notices to registered listeners
config.active_support.deprecation = :notify
# Setup for production - deliveries, no errors raised
config.action_mailer.delivery_method = :smtp
config.action_mailer.perform_deliveries = true
config.action_mailer.raise_delivery_errors = false
config.action_mailer.default :charset => "utf-8"
config.action_mailer.default_url_options = {
:host => 'www.****.com',
:protocol => 'https'
}
config.action_mailer.smtp_settings = {
:address => 'smtp.gmail.com',
:enable_startls_auto => true,
:port => 587,
:authentication => :plain,
:user_name => '***',
:password => '***'
}
end