VI3 hosts cannot be added if vCenter is licensed but License Server is not Configured

I had thought of playing with VC4.0 /ESX3.5/4.0 . I had VC4.0 and then from my VC2.5 I disconnect one ESX host and was trying to connect my VC4.0 . It was giving me error

I then checked license and found that it was added with IP address. I then added another VI3 license server using FQDN and then I was able to add ESX host into VC4.0