Filtering through my e-mail after a short, one week, holiday I ran into an e-mail from one of my colleagues pointing me to VMware KB Article 1013013. This KB article describes one of the first patches for vCenter Server 4.

The problem is that High Availability in a vSphere 4 virtual environment may not work when a host failure occurs and the node failure detection algorithm fails when using certain IP addresses. VMware found out that this is due to the fact that all of the Service Console Port(s) or Management Network IP address(s) on an 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.

The problem can obviously be solved by changing (one of the) Service Console Port(s) or Management Network IP address(s) or install vCenter Server 4.0 Patch 1.

More information can be found here.