Switching desktops

[Neil Winchurst]

Don't know why, but suddenly I am finding that I cannot use Control + a 
function key to switch desktops any more.

I have searched around but to no avail so far. Can anyone point me in 
the right direction please?

I can use the mouse on the panel to choose a desktop, of course. but I 
am used to using the function keys.

I am using.Kubuntu Hardy.

TIA

Neil Winchurst