datacenter.QueryConnectionInfo error when connecting ESX host

I had a bit of a problem in my home lab. I have 2 hosts, and one crashed. Unfortunately this was the host running AD & vCenter. When I brought the host back, I managed to restart the VMs, but looking in the vSphere client when I connected back onto vCenter, both hosts were disconnected. When I tried to reconnect, I got this Datacenter.QueryConnectionInfo error message. I have a feeling that name resolution was to blame here, but couldn't work out what was wrong. I could ping the hosts from vCenter by IP & name, I could add the hosts by IP address, but not by name. The only work around I could come up with was to add the ESX host details into the hosts file to avoid using DNS. As soon as I did that, I could reconnect the hosts. I've no idea what the actual problem is, although i wonder if some connection information is stored in the database and was corrupted when the host died.