Even if you have installed the updated ESX 3.5 Update 2, you may run into an issue where you see an HA error on your ESX Cluster. Specifically, you see an error such as:

Insufficient resources to satisfy fail over and unable to contact a primary contact HA agent.

This can occur if an ESX Server has capital letters in its hostname. To resolve, do the following an each server:

1. Type hostname to display the current FQDN.

2. If any capital letters are in the hostname, type hostname fqdn in lowercase

3. Edit the /etc/sysconfig/network file. The following would be the command to edit the file using nano. nano /etc/sysconfig/network

4. Restart the vmware management service using the command:
Service mgmt-vmware restart

Within a few minutes the HA configuration should disappear from the ESX Cluster. I contacted VM Support, who was aware of the problem, and was told a patch is currently in the works to correct this issue.