I have a question regarding card interactions, I may be overlooking some obvious rule but I don't think so.

So I'm playing mtgo and have a [[high priest of Penance]] out enchanted with [[gift of immortality]], opponent attacks with [[emrakul, the Aeons Torn]] annihilator triggers both priest and gift get sacrificed, gift triggers bringing back the priest  (this should all be during the attack phase if I'm not mistaken) before the declaration of blockers, however it didn't allow me to block emrakul with the priest  (which would have destroyed emrakul when the priest triggered). Is this a mtgo related issue or am I missing something?

Thanks in advance to anyone who has an answer.