After you apply a host profile to a new member of an HA cluster on vSphere, you may receive an error indicating that HA could not be made active on the new host. In your perusal of events in vCenter, you may run across this error:
Cannot complete command 'hostname -s' on host 192.168.1.1 or returned incorrect name format
If this happens to you, all it means is that you've not set the hostname for the new vSphere host and it's probably still set to "localhost." This is easy to correct.
Simply go to Configuration > DNS and Routing > Properties and enter the correct hostname.
Then, place the server into maintenance mode and remove it from maintenance mode. HA will restart and all will be well.