Alt+tab and Alt+F4 suddenly not working

[Paul Hunt]

Hey all,

Using Oneiric with all the latest updates and the extra a11y PPA...

I've suddenly found that the alt+tab and alt+F4 keystrokes aren't working.

I can still activate menus with alt+F etc.

It's not a hardware thing because if I reboot into Windows I can alt+tab 
and alt+F4 just fine.

I'm fairly sure that the session is still unity 2D as the launcher is 
working as before.

Please help!

Paul