rake db：createまたはrake db：migrateをローカルで実行すると、アプリは期待どおりにテーブルを正常に構築します。ただし、herokuで実行すると（たとえば、heroku rake db：migrate --trace --app）、突然次のエラーが発生します。
C:\>heroku rake db:migrate --trace --app foo rake aborted!
undefined method `task' for #<Foo::Application:0x7f8e77aa1420>
/app/.bundle/gems/ruby/1.8/gems/railties-3.0.4/lib/rails/application.rb:214:in `initialize_tasks'
/app/.bundle/gems/ruby/1.8/gems/railties-3.0.4/lib/rails/application.rb:139:in `load_tasks'
/app/.bundle/gems/ruby/1.8/gems/railties-3.0.4/lib/rails/application.rb:77:in `send'
/app/.bundle/gems/ruby/1.8/gems/railties-3.0.4/lib/rails/application.rb:77:in `method_missing'
/app/Rakefile:7
/app/.bundle/gems/ruby/1.8/gems/rake-0.9.0/lib/rake/rake_module.rb:25:in `load'
/app/.bundle/gems/ruby/1.8/gems/rake-0.9.0/lib/rake/rake_module.rb:25:in `load_rakefile'
/app/.bundle/gems/ruby/1.8/gems/rake-0.9.0/lib/rake/application.rb:495:in `raw_load_rakefile'
/app/.bundle/gems/ruby/1.8/gems/rake-0.9.0/lib/rake/application.rb:78:in `load_rakefile'
/app/.bundle/gems/ruby/1.8/gems/rake-0.9.0/lib/rake/application.rb:129:in `standard_exception_handling'
/app/.bundle/gems/ruby/1.8/gems/rake-0.9.0/lib/rake/application.rb:77:in `load_rakefile'
/app/.bundle/gems/ruby/1.8/gems/rake-0.9.0/lib/rake/application.rb:61:in `run'
/app/.bundle/gems/ruby/1.8/gems/rake-0.9.0/lib/rake/application.rb:129:in `standard_exception_handling'
/app/.bundle/gems/ruby/1.8/gems/rake-0.9.0/lib/rake/application.rb:59:in `run'
/app/.bundle/gems/ruby/1.8/gems/rake-0.9.0/bin/rake:31
/usr/ruby1.8.7/bin/rake:19:in `load'
/usr/ruby1.8.7/bin/rake:19
Rakefileを見ると、これがすべてです。
require File.expand_path('../config/application', __FILE__)
require 'rake'
Foo::Application.load_tasks
load_tasksの行は7行目です。何が変わったのかはよくわかりませんが、確かに何かが変わっています。誰かがこのエラーを経験したことがありますか？