One of many subdomains of a multisite is "unavailable"

One of many multisite subdomains is getting a “website unavailable” message. The site is http://annahuemmer.risd-sculpture.com whereas http://wpfolio.risd-sculpture.com/ and http://mikhailmishin.risd-sculpture.com/ and http://yanchen.risd-sculpture.com/ among 30+ others all work.

I have not changed the .htaccess file since the first installation. Nor have any of the settings been changed recently. http://annahuemmer.risd-sculpture.com worked until a few days ago. Both the front end and the back end worked fine.

I find this to be a very strange problem and am not sure of the cause – something on the site, something related to the server or… This multisite has been running perfectly fine for 3+ years. And I have searched for solutions to related problems and have found none.

Thanks for your time.