Many customers are hitting a new bug in ESX preventing them from powering on virtual machines or VMotion them.  There is a published knowledge base article on this which reads>>

Unable to Power On virtual machine with “A General System error occurred: Internal error”

A virtual machine fails to power on, fails to leave suspend mode, or fails to migrate with VMotion and the following message is displayed in the vmware.log file for the virtual machine:

This product has expired. Be sure that your host machine’s date and time are set correctly.
There is a more recent version available at the VMware web site: http://www.vmware.com/info?id=4.
————–
Module License Power on failed.

Currently running virtual machines will continue to run but will not be able to perform migration with VMotion, suspend or power on virtual machines.

Read more »

With the new Virtualcenter 2.5 Update 2 comes some tighter restrictions on HA network configurations.  This error message commonly occurs when the nodes in a cluster contain incompatible networks. An attempt to reconfigure clusters might fail now if they do not have identical networks.

Some customer are reporting the message:

HA agent on <esxhostname> in cluster <clustername> in <datacenter> has an error Incompatible HA Network:
Consider using the Advanced Cluster Settings das.allowNetwork to control network usage.

VMware has just published two Knowledgebase articles for this issue.  KB 1006606 covers the network compliance check, which will also link to KB 1006541 covering how to address the issue.  

I am also told VMware is working to have this included in the Update 2’s release notes.

As soon as Update 2 of Virtualcenter 2.5 hits the streets we started getting calls into support lines here at VMware about HA breaking.

Common reports include:

“insufficient resources to satisfy HA failover level on cluster” and “unable to contact a primary HA agent in cluster”

We think we know what is causing this, so I’m sharing this here in hopes of saving you a call.

The key is that all of your hostnames are in lower case only.

So, in Virtualcenter check-
-each host in the cluster, go to the configuration tab, DNS and routing, hostname
-everything needs to be lowercase
On each one of your ESX hosts-

ssh into each host and check-
-lower case names only in /etc/hosts
lowercase names only in /etc/sysconfig/network
cat /proc/sys/kernel/hostname

if not correct :

hostname <FQDN>

after this you can check the settings are correct using-

uname -n
hostname -a
hostname -s
hostname -d
hostname -f
hostname

in addition to this also make sure hostname in /etc/vmware/esx.conf is lowercase-

/adv/Misc/HostName = <FQDN in lowercase>
when done enable HA on cluster again.

Check this link if you are seeing the HA incompatible network message.