Restful web service error on saving record

Error is:
NoMethodError: You have a nil object when you didn't expect it!
You might have expected an instance of ActiveRecord::Base.
The error occurred while evaluating nil.[]
        from /www/gems/gems/activeresource-2.0.2/lib/active_resource/
base.rb:817:in `id_from_response'
        from /www/gems/gems/activeresource-2.0.2/lib/active_resource/
base.rb:804:in `create'
        from /www/gems/gems/activesupport-2.0.2/lib/active_support/
core_ext/object/misc.rb:28:in `returning'
        from /www/gems/gems/activeresource-2.0.2/lib/active_resource/
base.rb:803:in `create'
        from /www/gems/gems/activeresource-2.0.2/lib/active_resource/
base.rb:636:in `save_without_validation'
        from /www/gems/gems/activeresource-2.0.2/lib/active_resource/
validations.rb:262:in `save'
        from /data/www/rails/authentication/app/models/account.rb:
89:in `create_notification'
        from /www/gems/gems/activerecord-2.0.2/lib/active_record/
associations/association_proxy.rb:125:in `send'
        from /www/gems/gems/activerecord-2.0.2/lib/active_record/
associations/association_proxy.rb:125:in `method_missing'

Client:
notification_email.rb model
class NotificationEmail < ActiveResource::Base
  self.site = "[http://mysite]"
end

I use the model class to create a new object. Error happens on save.
def create_notification
       n = NotificationEmail.new
       n.save
end

Web service set up is very simple. It basically saves the record to
the database. I tested it with curl and it works. Anyone has any
ideas what this error message means?

Thank you!