translation missing: en.date.formats.default

Getting a strange error on missing translation.

I18n.l(Order.first.created_at.to_date)

I18n::MissingTranslationData: translation missing:
en.date.formats.default

But if try this:

I18n.l(Order.first.created_at)

"2011-11-26 13:25:21 UTC"

this is in my config/locale/en.yml
en:
  date:
    formats:
      default: "%Y-%m-%d %H:%M:%S %Z"

Any thought on why I am getting this error? thanks.