What you don't want to see when your install SQL Server in a clustered environment !

This happened because the server was missing .Net Framework 3.5 service pack 1, so I flipped over to the "features" and added this feature, re-ran the "check prerequisites" and completed the install, or so I thought.

But then suddenly the windows update kicked in, as it detected that there were existing approved patches for this new feature, and immediately pushed those down.

The key here is to quickly flip over to services and stop the windows update service, of course this assumes your group policy allows you to stop that service.

Which will finish first SQL Server install of adding a node to a cluster or the remaining time to reboot !