Notification area not functioning correctly

> For some reason I have lost the ability to use the "Hide
> when inactive" function on the notification area.
> Taskbar properties shows the option as selected but there
> is no "Hide / Unhide" icon on the taskbar. It is as if I
> have de-selected "Hide inactive icons". Any ideas on how
> to fix. The only change that I have made is to load the
> lastest version of Zone Alarm Firewall. I didn't notice
> this issue before that.
>
> Thanks