Not possible to enable Secure Pages with Nginx

I have Secure Pages 7.x-1.0-beta2 installed on two Drupal sites running on Nginx. I applied the 2 patches listed on the project page. I have also tried applying the suggestions listed in this article:

http://www.metaltoad.com/blog/running-drupal-secure-pages-behind-proxy

1. settings.php

if (isset($_SERVER['HTTP_X_FORWARDED_PROTO']) &&
  $_SERVER['HTTP_X_FORWARDED_PROTO'] == 'https') {
  $_SERVER['HTTPS'] = 'on';
}

2. nginx vhost file:
location / {proxy_set_header X-Forwarded-Proto $scheme;}

The option remains greyed out even when I visit the link to use if the test has failed. I have Secure Pages enabled on three other Drupal sites that are running on Apache no problem. Am I missing something?