Membership: user registered but subscription not completed

I have a set-up with the WP 3.9.1 and latest version of Membership.

When a user signs up, the registration completes successfully, but it then sits there showing this url http://www.ibsregister.com/register/?action=registeruser&subscription=1 and any attempt to access the website itself just sits there too!

I am using BuddyPress extended profiles, but turning this off doesn't appear to make any difference.

I have another very similar setup (egtauk) on old versions of everything and that works fine