Yes, I do see a duplicate content problem with the domains. Try a 301 redirect of your domains so that www.domain.com and domain.com land to the same domain.

Also, your drop is probably in long tailed keywords. Have you stopped doing something you were doing ? Maybe a ppc campaign or haven't done a press release lately? I see you have many press releases, and those could have contributed to a lot of long tailed keywords for you..