Increased functionality and virtual machine control in the Windows Server 2008 Failover Cluster Management console for the Hyper-V role
This update changes the Failover Cluster Management console (the Cluadmin.msc file) and the server components of the failover cluster. If this update is installed on one node, it should be installed on all nodes of a Windows Server 2008 failover cluster. It may be installed on one node at a time. However, we recommend having all the nodes updated in a reasonable time. You may experience errors on a Failover Cluster Manager that has not been updated to a failover cluster that has had this update applied. These errors occur because of differences between the non-updated Cluadmin.msc file and the updated failover cluster.
More info: KB951308