Blacraft Forum

Some info:

Last updated on 22/9/2013 18.04.00 by Miiuku
The Minecraft session servers are currently down, which is causing all servers to currently be unreachable. There is nothing we can do about this issue other than wait for Mojang to bring their servers back online. We apologize for any inconvenience this is causing.

To check the current status of the servers, visit Mojang's help page.
https://help.mojang.com/

Update: The session servers are up and running and appear to be stable.
Update: Mojang's servers appear to be in Purgatorial state between Offline and Online, users may or may not be able to login/update and connect to servers.

Anyway I restarted the server and I think it's up now, but it seems to be running on 1.6.4 and I have 1.6.2 so can't test.