I just received word on this from Admin because one of my hubs got hit with "sub-standard." In the past it has been within the terms of service to post your own original content on Hubpages that had also been posted elsewhere on the internet. Apparently that has changed going forward. This did take me by surprise because it's never been the case before, and when I read the updated TOS I used the commentary at the bottom to determine which sections had been revised and needing my attention, and those did not discuss the duplicate content issue. Obviously I need to head back and read it all through much more carefully.
At any rate, if you have published the article on more than one site, that's why it's been pulled. If you haven't posted it on more than one site, then I'd suggest running the entire thing through a plagiarism checker such as the one at dustball.com. This will give you links to searches containing phrases in your article that are repeated on the web, and may help you find someone who is plagiarizing your work.