Error Updating VUM vCenter Update Manager From 5.1 to 5.5

Running the update for vCenter Update Manager 5.5 from 5.1 on a WIndows 2008 R2 server after upgrading all the other components I was receiving an error like below and couldn't click next in the installer to get past the credentials page:

validation failed for service account user

setup failed credentials could not be validated

Looking in the install log vminst.log in %temp% showed the following but wasn't particularly useful:

process returned 199

Error:: unknown VC error

To get past this I checked if the service account for VUM can log in to vSphere client, I couldn't.  I then added the service account explicity as an administrator at the vCenter level with inheritance to be able to login to vCenter.  I could now validate the credentials for the install and complete it.

After completing the upgrade I had to change the update manager service in Windows to run as the service account.