I have a mixed ESX cluster at home. One box is running ESX 3.5 the other box is running ESX 4.0. When I tried to enable HA on this cluster I got the following error:
The ESX 3.5 host has a second Service Console port on the Storage (iSCSI) lan. The ESX 4.0 host doesn’t need this so this is why the ESX 4.0 host got this error.
To solve this issue I created a second Service Console Port on my ESX4.0 server.
Now I was able to enable HA on Cluster.