Have you got:
Code:

---

Section "ServerFlags"
...
        Option          "Allow VTSwitch"
...
EndSection

---

set in /etc/X11/xorg.conf ?

Or try this:
http://lists.freedesktop.org/archives/xorg/2004-September/003473.html

I think it may have been a keyboard config thing - I have a UK Microsoft keyboard....

my xorg.conf looks like this now:
Code:

---

Section "InputDevice"
        Identifier      "Keyboard"
        Driver          "kbd"
        Option          "CoreKeyboard"
        Option          "XkbRules"      "xfree86"
#       Option          "XkbModel"      "pc105"
        Option          "XkbModel"      "microsoft"
        Option          "XkbLayout"     "gb"
#       Option          "XkbGeometry"   "microsoft"
EndSection

---