Separate names with a comma.
I just tried unmounting backup disks as well and the patch worked immediately after that.
Re my message from a few minutes ago about the PDMU4021 patch, I see that there is a separate thread on that problem, which I will check into....
Thanks Lance. I did try that and it does seem to get me further (appears to download something, asks for admin password) but then fails almost...
I have the same issue - same message and the updater.plist file mentioned in the KB article does not exist.