www.claimid.com is not an OpenID 2.0 Provider. It only supports OpenID 1.1. Therefore, typing www.claimid.com into an OpenID relying party will not work (OpenID 1.1 does not include identifier_select functionality, which is what you're trying to do). You have to type in the individual's OpenID. Try typing in claimid.com/aarnott and it will work just fine.
myopenid.com on the other hand is an OpenID 2.0 Provider, which is why you see that one working for you.