VMware has released vCenter Server 4.0 Patch 1 to address an issue with VMware HA. From the VMware KB:
You experience these symptoms:
- In vCenter 4.0, VMware HA might not failover virtual machines when a host failure occurs.
- When the ESX host’s IP address in a VMware HA enabled cluster is configured with certain IP addresses, the node failure detection algorithm fails.
- You are susceptible to this issue when all of your Service Console Port(s) or Management Network IP address(s) on your ESX host fall within the following range:
3.x.x.x – 9.x.x.x
26.x.x.x – 99.x.x.x
Note: You are not affected if one of Service Console Port(s) or Management Network IP address(s) on your ESX host falls outside of this range.
More information on: http://kb.vmware.com/kb/1013013
Posted by Ted Steenvoorden 
