I know sometimes this happens when programmers do maintenance or make changes to a site without shutting it down for long periods of time so that people still have access to it. Maybe that's the problem?
On a similar note, I have seen someone say that the site always shuts down (something about a database error?) around 1:00am. I'm assuming that's their time for where ever they live in the world, whatever that time is for other people the exact time will vary. (weird wording I hope you get what I mean)