Singleplayer server is down, happens now and then. Wait a few hours and try again. They should kinda fix it :|
It's a known bug with the single player system that only happens at a certain time of day. The devs are aware. Best you can do is play or spectate ladder while you wait.
As Apostate stated this is a known bug we are looking into. There are a lot of logistics involved with this one which is slowing down the process in resolving this issue. Today, we unfortunately had a bit of a longer outage than normal.
