No 'add certificate' button in apple iOS provisioning portal

I am trying to follow the steps to create a "Distribution provisioning profile". I get here and the instructions tell me to "click the ‘Add Certificate’ button", but there is no button :-( (nice one apple) I can see from the (similar) unanswered SO question here that others have this problem. I also recall that I have had this problem before, but I can't remember how I solved it. I am using a mac, running safari. How do I get a button? Help!?

I found an answer to this here the key information was "if you already have a certificate, this option will be unavailable as you need only one". Really useful information that.