Keys to change layout for switching language

[David Shwatrz <dshwatrz gmail com>]

Hello,
I have gnome 3 on Fedora 15; I added another language.
On the panel there is in indicator  to the new language.
I had assigned a key combination to switching languages:
In keyboard preferences->Layouts->Options, "in Keys to change layout,"
"Both control keys" checkbox is selected. However, when I press both
control keys,
the language is **not** changed. I must add that by clicking the mouse on the
language indicator, the language **does** change!

what should I do ? any advice ?

rgs,
DS