RinguGoofs
Continuity
At the beginning of the movie, the TV in Tomoko's room is on. However, in the next scene when Tomoko has a close up, it's off. Neither Masami or Tomoko had switched it off.
Factual errors
One the pictures received from the photo shop shows a date, August 29, 1997. Later on the story tells "September 13, Monday". September 13, 1997 was Saturday.
Revealing mistakes
In a close-up of Sadako in the end scene, one of her fake finger extensions is coming off.