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In that email the client states that the site is down and will be for the next 72 hours. He forgot to renew his domain with Verio. The email address that Verio had on file was incorrect.
One of the things you should add to your list of priorities when promoting a site, is to check the expiration dates on any domains associated with your campaign. Also verify that the contact email addresses are correct. Don't assume that the client has taken care of this.
It's a first for me, but I've seen many topics crop up around the subject. I'm not sure how much damage will be done and can only wait and see. This is a site that has thousands of top ten positions across the board. I will now spend the day double checking all of my clients domain expiration dates just to be on the safe side!