A thread at WebmasterWorld has a recent chronological time line of the technical issues Microsoft adCenter advertisers had to deal with since August 28th. It got better and then got worse and then got better.
The system went down again yesterday at 11:30am and came back online about 1:30PM the same day.
I guess these things are just beginner kinks that still need to get out of the system.
Forum discussion at WebmasterWorld.