Paperclip Error: method_missing': undefined method `before_avatar_post_process'

Hello im just trying to run a simple migration to add header_image to my user model.

When i run the below migration:

rails generate paperclip user header_image

I receive this error:

/Users/joseph/.rvm/gems/ruby-2.1.2/gems/activerecord-4.2.0/lib/active_record/dynamic_matchers.rb:26:in `method_missing': undefined method `before_avatar_post_process' for User (call 'User.connection' to establish a connection):Class (NoMethodError)

Anyone know how to fix?

Paperclip is definitely installed.