Carrierwave gem に問題があります。
簡単な rake コマンドをいくつか実行すると、システムで次のエラーが表示されます。
Starting process with command `bundle exec rake jobs:work`
2013-03-18T21:50:07+00:00 app[worker.1]: /app/vendor/bundle/ruby/1.9.1/gems/bundler-1.3.2/lib/bundler.rb:343:in `rescue in eval_gemspec': There was a NoMethodError while loading carrierwave.gemspec: (Bundler::GemspecError)
2013-03-18T21:50:07+00:00 app[worker.1]: undefined method `today' for Date:Class from
2013-03-18T21:50:07+00:00 app[worker.1]: from /app/vendor/bundle/ruby/1.9.1/gems/bundler-1.3.2/lib/bundler.rb:332:in `eval_gemspec'
2013-03-18T21:50:07+00:00 app[worker.1]: /app/vendor/bundle/ruby/1.9.1/bundler/gems/carrierwave-0206f800dc6f/carrierwave.gemspec:12:in `block in <main>'
2013-03-18T21:50:07+00:00 app[worker.1]: from /app/vendor/bundle/ruby/1.9.1/gems/bundler-1.3.2/lib/bundler.rb:312:in `block in load_gemspec_uncached'
2013-03-18T21:50:07+00:00 app[worker.1]: from /app/vendor/bundle/ruby/1.9.1/gems/bundler-1.3.2/lib/bundler.rb:307:in `load_gemspec_uncached'
2013-03-18T21:50:07+00:00 app[worker.1]: from /app/vendor/bundle/ruby/1.9.1/gems/bundler-1.3.2/lib/bundler.rb:297:in `load_gemspec'
2013-03-18T21:50:07+00:00 app[worker.1]: from /app/vendor/bundle/ruby/1.9.1/gems/bundler-1.3.2/lib/bundler/source/git.rb:174:in `load_spec_files'
2013-03-18T21:50:07+00:00 app[worker.1]: from /app/vendor/bundle/ruby/1.9.1/gems/bundler-1.3.2/lib/bundler/lazy_specification.rb:52:in `__materialize__'
2013-03-18T21:50:07+00:00 app[worker.1]: from /app/vendor/bundle/ruby/1.9.1/gems/bundler-1.3.2/lib/bundler/spec_set.rb:85:in `map!'
2013-03-18T21:50:07+00:00 app[worker.1]: from /app/vendor/bundle/ruby/1.9.1/gems/bundler-1.3.2/lib/bundler/source/git.rb:149:in `specs'
2013-03-18T21:50:07+00:00 app[worker.1]: from /app/vendor/bundle/ruby/1.9.1/gems/bundler-1.3.2/lib/bundler.rb:307:in `chdir'
2013-03-18T21:50:07+00:00 app[worker.1]: from /app/vendor/bundle/ruby/1.9.1/gems/bundler-1.3.2/lib/bundler/source/path.rb:115:in `each'
2013-03-18T21:50:07+00:00 app[worker.1]: from /app/vendor/bundle/ruby/1.9.1/gems/bundler-1.3.2/lib/bundler/source/path.rb:115:in `load_spec_files'
2013-03-18T21:50:07+00:00 app[worker.1]: from /app/vendor/bundle/ruby/1.9.1/gems/bundler-1.3.2/lib/bundler/source/path.rb:116:in `block in load_spec_files'
2013-03-18T21:50:07+00:00 app[worker.1]: from /app/vendor/bundle/ruby/1.9.1/gems/bundler-1.3.2/lib/bundler/spec_set.rb:88:in `block in materialize'
2013-03-18T21:50:07+00:00 app[worker.1]: from /app/vendor/bundle/ruby/1.9.1/gems/bundler-1.3.2/lib/bundler/definition.rb:148:in `requested_specs'
2013-03-18T21:50:07+00:00 app[worker.1]: from /app/vendor/bundle/ruby/1.9.1/gems/bundler-1.3.2/lib/bundler.rb:120:in `setup'
2013-03-18T21:50:07+00:00 app[worker.1]: from /app/vendor/bundle/ruby/1.9.1/gems/bundler-1.3.2/lib/bundler/setup.rb:17:in `<top (required)>'
2013-03-18T21:50:07+00:00 app[worker.1]: from /app/vendor/bundle/ruby/1.9.1/gems/bundler-1.3.2/lib/bundler/definition.rb:159:in `specs_for'
2013-03-18T21:50:07+00:00 app[worker.1]: from /app/vendor/bundle/ruby/1.9.1/gems/bundler-1.3.2/lib/bundler/environment.rb:18:in `requested_specs'
2013-03-18T21:50:07+00:00 app[worker.1]: from /app/vendor/bundle/ruby/1.9.1/gems/bundler-1.3.2/lib/bundler/source/path.rb:86:in `local_specs'
2013-03-18T21:50:07+00:00 app[worker.1]: from /app/vendor/bundle/ruby/1.9.1/gems/bundler-1.3.2/lib/bundler/spec_set.rb:85:in `materialize'
なぜそれが起こるのか誰にも分かりますか？