Daniel,
Generally, try to create a new thread for support unless your topic is definitely related to the others. In this case, the symptom may be similar, but I believe the problem is very different.
There seems to some weird redirecting going on on your site that I think is the problem. If I go to
www.polyorganic.com.br/ (with the www.), and I look at the HTML on the page, all the links go to the non-www version. That's not normal for Joomla to do that. Additionally, when I login using Facebook from the www. version, I'm redirected to the non-www version (again, not normal).
I am seeing the error you mention, but only from the non-www URL for the site. To fix this, my guess would be to edit your Facebook application and update the Website url to
polyorganic.com.br/ (non-www) and make sure the domain/namespace setting is polyorganic.com.br
Hopefully, all the above will help you track down the problem.
Good luck,
Alex