I get the same error. And I doubt that will be the URL for the "official" Web site because all of Warner Brothers' films seem to have a specific type of URL. For example, Harry Potter's is harrypotter.warnerbros.com and Batman's is thedarkknight.warnerbros.com. So the official site for DS should be
http://darkshadows.warnerbros.com - and that site isn't available either.
Now, someone also connected to the film could be planning
http://www.darkshadowsthemovie.com/ - but if they are, apparently the site isn't up and running.
Thanks for sharing the info, though.
It may yet pan out...
126 days 5 hours 16 minutes 2 seconds until the day the Depp/Burton Dark Shadows is released(ET)!!