An update today (30-11-2012) on 12.4 lead to failure to log in. The system gets through its boot process then presents the logins, on choosing any of these immediately returned to log-in screen with no error. Machine is an AMD FX 64 on an Asus MB using the built-in graphics. If no one knows what this might be, what's the alternative distro to Ubuntu? It's the second time something like this has happened after an update in three months, kudos to the Ubuntu team but I need more reliability. Cheers, thanks to all.