What this really refers to is gnome-volume-control-applet which is what controls the volume in the panel/indicator applet.
In Ubuntu 10.04 it is just the applet mentioned above, run that from the command line and it will start.
I lost mine when I removed pulseaudio trying to fix audio issues with Flash and Opera. It also removes the gnome-volume-control-applet from starting. *Ialso note........