I enabled HA on a new cluster the other day and one of the hosts came back with the following error:

Cannot complete the configuration of the HA agent on the host. Misconfiguration in the host network setup.

On ocassion, I have seen weird HA errors where simply selecting the 'Reconfigure for HA' on the host fixed the issue. I tried this, but the same error was seen. I next selected the host and went to Tasks & Events - Events. From there, I found the following error message:

HA agent on <host> in cluster <cluster> in <datacenter> has an error: Cannot complete the HA configuration. 

Selecting the message and under Related Events selecting Show displayed:

Host <host> has the following extra networks not used by other hosts for HA communication: <IP>,.
 Consider using HA advanced option ads.allowNetworkto control network usage.

Looking at the VMkernel interface, everything appeared to be configured correctly. I ensured the IP configuration was correct and that no duplicate IP issue was being experienced. So what was causing the problem?

Looking at the VMkernel interface again, I realized that for some reason the interface was selected as a Management Interface. Since a Management interface already existed and all other VMkernel interfaces in the cluster did not have this option selected, I figured I found the problem. I removed the checkbox and then selected 'Reconfigure for VMware HA' and the problem was solved. This is a great justification for using host profiles to ensure all hosts are configured identically.