Thanks to everyone who replied with suggestions. 'id -Z' just returned "user_u:system_r:unconfined_t" both for a user and root. I relabelled the filesystem and rebooted. There are no new updates today, but installing a package worked correctly (I first saw the message when installing a new package). I then tried downgrading a package by hand and ran 'sudo yum update' and that also worked fine. I'm not quite sure why the problem has gone away. Maybe an updated package yesterday fixed it, or maybe relabelling did the trick (there do seem to have been a lot of new "policy" packages recently). I'll be sure to report if I have any further problems. Jonathan -- http://jonathan.rawle.org/