Andrea,
Not sure why it would work for Like and not Comments. The same code is used for both, so it really shouldn't be different once you got one working. Can you check to make sure AUP is setup properly to award points for the new comment?
Beyond that, I tried to go to one of the direct links for your site, so it's not in the Facebook Canvas, to test. I was automatically redirected to the App page though. That makes it difficult to diagnose things. Can you disable the auto-redirect so we can go to the page directly? Also, let us know what the current direct URL is (it seems to change).
Thanks,
Alex