partial problem

You have not provided any explicity action to form_tag in your
partial. That means it will post back to its current URL. When you're
on the login page, I'm guessing that it works fine, since it will POST
to the /login/login action. However, anywhere else on your site it
will not work.

Provide an action to that form_tag and it will work. [i.e. form_tag
'/login/login']