I wanted to work with vSphere Replication today, to write an article on it in fact, but first I had to upgrade everything to vSphere 5.5 Update 2. The vC I use is the vCSA so that upgrade was easy and smooth. But when I went to use VUM to upgrade my hosts I had the error mentioned above returned very quickly.
It was confusing so I checked the events and found this.
Where I saw quite clearly that I had forgotten to do something.
I forgot to enable the disable HA admission control. Once I did that the VUM update went great.
I made this mistake to empower you to avoid it.
Michael
=== END ===
Notes from MWhite 