A lesson that I learned while setting up our new data center for work, is to be careful when setting up your clustered servers.
Most of our servers are VMs, including a Windows 2008 Cluster (yeah I know not supported, I’m a rebel damn it and I want a Windows 2008 cluster installed under VMware ESX).
When I was setting up my VMware templates I decided to save myself a step and I added the fail over clustering support to the template, as all VMs which would be running Windows 2008 Enterprise would be clustered. Apparently this causes a problem as when the fail over clustering is installed it creates a few network adapters which are hidden with unique MAC addresses. However when you then deploy that template as a VM, the MAC address isn’t changed which then causes the validate wizard to fail as having unique MAC addresses is a requirement to create a cluster.