As per the topic title
Click the upgrade link in the yellow warning bar in admin
Click Upgrade Automatically (has always worked on this install in the past)
Message "Unpacking the Update" appears, and stays, and nothing progresses.
As far as I know, nothing has changed on the server, and no additional plugins since last successful auto-update (in fact I knocked out a couple of them and deleted them, so less memory load which should have improved auto-updating ability).