Setting Custom error message with CarrierWave

Actually it is:

en:
  errors:
    messages:
      extension_white_list_error: "You are not allowed to upload %{extension} files, allowed types: %{allowed_types}"

Source:

https://github.com/jnicklas/carrierwave/blob/master/lib/carrierwave/locale/en.yml

If someone ends up here in 2016+ and wonders why correct answers found on this page or anywhere else in the web do not work, it could be because of this. At least it was in my case:

Rename extension_white_list ~> extension_whitelist

Easy thing to miss when just copying solutions.

https://github.com/carrierwaveuploader/carrierwave/commit/06003a5044190f93d07d958b6ca9fd6f6f8fbdb2