Hi, I had the same thing yesterday,
i've upgraded the fedora 8 kernel from 220.127.116.11-27.fc8 to 18.104.22.168-40.fc8
and my wifi did not longer work.
The networkmanagers finds the networks, but when I try to connect it is as if the password is not ok
and asks me again for the wpa shared secret.
Rebooting the same laptop under vista works with wifi fine.
Then I suspected it was due to the kernel upgrade, and in the bootloader I've selected the old kernel
and it works again
Hope it will be fixed in the next kernel !