This literally just happened to me.
I don't have DNS configured right, tried to trick the hosts file. This happened.
It was fixed when I opened vCenter and added the ESXi server by IP rather than FQDN.
I bet if you are on your vCenter (sshed or RDPed in or whatever) and you try to nslookup <ESXIserverFQDN> you won't get a result. Or if you do, I bet nslookup <ESXIserverIPADDRESS!> won't work.
Add by IP and make sure DNS works both ways (name and reverse resolution too) and youll be good.
