ALT-TAB no longer working?

[Scott I. Remick]

So I sheepishly post here because I suspect it's simple/dumb, but all my
Google-searching last night came up empty. :( But anyways... as far as I
can determine, my ability to alt-tab to task-switch broke during my
upgrade from Gnome 2.12 -> 2.14 and I can't for the life of me figure out
what handles that or find any knob/button/tweak to fix it. Any thoughts?
Be nice... :)