In an attempt to fix the problem, I uninstalled lightdm and gdm is now the default. But I experience the same problem with gdm. When I try to reinstall lighten, I receive:
WARNING: The following packages cannot be authenticated! lightdm Install these packages without verification [y/N]? y Err http://us.archive.Ubuntu.com/ubuntu/ raring-updatea/main lighten amd64 1.6.0-ubuntu3 Something wicked happen ed resolving 'us.archive.ubuntu.com:http' (-11 - System error) Failed to fetch http://us.archive.ubuntu.com/Ubuntu/pool/main/1/lightdm_1.6.0-0ubuntu3_amd64.deb So me thing wicked happened resolving 'us.archive.ubuntu.com:http' (-11 - System error) E: Unable to fetch some archives, maybe run apt-get update or try with --fix missing?