It means no pages. Most likely the DC has been taken offline. I'm seeing about 10 offline dc's right now on the whole list.
I wonder if that would not explain the disappearance of indexed pages. How about if your pages index is on those Data Centers? (I know that the index is distributed over a number of Data Centers) I also see in my logs, google visits from Data Centers with IP's that Awstats doesnt recognise as google.
I've had the same problems in one of my sites.. Dropped from 100's of links down, down to few main pages indexed, down to just the index page. This happened a month ago and unfortunetely i have seen no movement at all as other people have. No bouncing up and down as other people have reported. Hopefully this will be fixed soon, but after waiting for over a month i haven;t got my hopes up..