I think I had similar problem. After "clean" installation of Kubuntu feisty beta amd64, nvidia driver did not work. After a full update the problem was fixed.
However, I still have an error message in Xorg.0.log: (EE) Failed to load module "wfb" (module does not exist, 0) -- after upgrade NVidia driver stoped working with following error: Failed to load module "wfb" (module does not exist, 0) https://launchpad.net/bugs/96600 -- ubuntu-bugs mailing list [email protected] https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
