It seems you haven't visited the forum in the last 48 hours.
You would have seen a notice that appeared on all forums on the n4 server that said that routine maintenance would take place from 09:30 (GMT +1) today and we should expect the down time to last six hours.
I understand from an earlier post on this forum that all Nabble forums are being moved to improved servers. This is being done on a server by server basis. It's n4's turn today.
No doubt it will happen to others over the coming days.
Just a Volunteer Nabble Helper - because the nice folk at Nabble have helped me! GregHelp - Building a set of answers to Nabble FAQs.