Redirect loop checkout page

Hi there,

I have been able to use WooCommerce successfully, but for some reason, now I can’t enter the “Checkout” page. I get a redirect loop error. It’s the same in all browsers.

Tried
Tried logged in as different users
Tried disabling what seemed like relevant plugins
Disabled W3 Total Cache
Tried creating a new page and adding the shortcode, setting the new page as the checkout in WooCommerce settings

Perhaps…
Got SSL but there is a certificate chain error in Safari and Firefox (Chrome accepts it)
Got redirect loop errors 1 other place at the site: Paid Membership Pro member account linking to Theme My Login “Profile”

Setup
I am hosted with Rackspace
Wordpress is updated
WooCommerce is updated

Any help is welcome.

Thanks,
Emil

https://wordpress.org/plugins/woocommerce/