I'm having the same problem as well, it's not entering Sin, I don't have problem with that, but I cannot enter Besaid, Baaj Temple and I cannot see the ending, after I beat Yu-Yevon, the screen flashes for a long time. I was thinking of beating Dark Valefor and catches 10 of every monster in Besaid but...... and I was also thinking of meeting Fayth of Anima but....... AND I was also thinking about seeing the sad ending again which I see from my friends data.

The reason why I highlighted the temple is because I cannot enter the temple not the pool.