Can't select power button action in 10.04

I am running 10.04 on a Desktop computer with an Atom D510 processor (motherboard: Intel BLKD510MO mini-ITX Socket775 BULK). I use it as a server, so it has no keyboard, mouse nor screen attached. I access it via ssh and remote desktop (via vncserver which I start manually). Becasue it has no monitor attached, X doesn't start automatically, but in other respects it is a fairly standard Ubuntu 10.04 setup.

I had set my Power Button to "Shutdown" in the Power Management GUI and
had no problems using this functionality. One day last week I had no response when
I pressed the power button. I then discovered that the drop down box
(in Power Management) where I was previously able to select from "Ask Me", "Hibernate"
"Suspend" and "Shutdown" only had the "Ask Me" option available (other
options had disappeared). How can I restore the other options?

It appears that a recent (automatic) update has cause the problem. I
have tried reinstalling pm-util and also to run with pm-utils not installed.