I still can't log in today either. I rang the helpline yesterday and was passed to a girl in the Uk who had no interest in the problem and all she suggested was restarting the computer which obiously hasn't worked
Figured it out, it is an issue with opendns. Setting your DNS to Google 8.8.8.8 and 8.8.4.4 sorts the issue. This is something you would not expect most people to know.
It appears that UB have changed the ip address of their server and this change has not fed through to certain DNS providers. The issue would eventually resolve itself over a few days as all the DNS providers are updated.