This request is AJAX so we can't use flash[:error]. Look at views/release_notes/update.js.erb -- what's happening is that the partial issues/release_notes is being rendered on the server side, and some HTML is pushed to the client, replacing the contents of #release_notes.

Since we use `error_messages_for` in `issues/release_notes`, we can just add this error to the release note's `ActiveRecord::Errors` object -- something like `@release_note.errors.add(:base, format_release_note_errors(...))`

Also is `format_release_note_errors` defined? Have you tried to get it to run through this code path? Try loading the issue page with a particular user, then taking away their edit issues privilege, then trying to update the release notes.