It should be a shortable stock now, however, there has to be available shares to short(borrow) as of now, too many shorts have borrowed as many shares to short as your broker has. Try a fewer amount of shares and see if it goes through.
Did you really belive you could make some money with this scam?
And this after 8 years they have used their traditional medias to convince other people that FB is essential? that even big companies HAVE TO be on FaceKook, when in fact 90% of their users are prepubertal teenage girls running multiple identities?!!!