I've had this same issue on another site. Users are registering for an account through Membership2 Pro. They then appear active in Admin (not Visitor) but with no payment made yet.
I most recently had a user that was "Active" in Admin, but when he tried to pay he said a "Test" sign would come down and not allow him to enter his payment.
Any ideas what this could be? I can't afford to have users gain access to my protected content without paying, or be unable to pay.