Update 6.05pm
Problems have been solved.
Update 4.45pm
Just to make everything worse, the thread information stored in our database corrupted while trying to resolve the original problem. The database has been repaired and restored, and work will continue to find the source of the problem.
Trouble Ticket 12.25am
The domain name just vanished from the serverside setup around midnight between saturday and sunday. It's being investigated and will be resolved as soon as possible. In the meantime the old URL has been made active again for the time being.
Sorry for any trouble.