I created a custom signup form. I chose a product that requires another product to already be purchased. Because I'm not logged in (I was testing), I got an error message. But there is no way, from there, to log in to fix the problem! I'd like to put a link under the error to the /login page, but editing _error.phtml seems to have no effect. Even after being successfully logged in, I still get an error on my signup page!