I have the same problem. After update manager 6 was installed successful, i went into vsphere client --plugin, saw the update manager client. installed it and it went fine. after the installation, i got this message:
"there was an error connecting to vmware sphere update manager - vcenter:443
database temporily unavailable or has network problems."
funny thing is in web client, i can see the update manager and able to setup baselines, etc.
why wouldn't it work in vsphere client?