Before, I use BB2 forum, it is able for guests to view and click to like button on the top of topic. Then I've changed to use Invision, it hasn't viewed for guests.
I've tried to turn again use BB2. But meet the same problem. 

Did I setting whatever wrong? How should I do? Thank!

Please post a link to a topic that guests can see on your forum.

My current forum http://learn.forumvi.com no longer show facebook like anymore even though I turn back to use BB2.
However, my another forum is use BB2. The FB like work well
http://jianxia2.forumvi.com/t4-topic

You say that you turned back to phpBB 2, but your forum's version is Invision.

Have you checked to see if the option had been deactivated in the administration panel?

Yes. I have. I see my forum as guest (logout) but it was no have like button.
Then I try to use again Invision.