Other mistake: When Sidney is on the set with her mother's covered body, it rises up and reaches for her, speaking in her mom's voice. Sidney calls out for Dewey before climbing out of the window. However, when she's grabbed, she yells out her own name: Sidney.
Other mistake: Ghostface has a strength that rivals a superhero. He's trapped under a bookshelf but not only gets free in a second; the mere gesture of freeing himself sends a grown, bigger man flying and tumbling over a desk. Seriously, from the angle it appears that the case hit Cotton in the side of the head, but that would never propel him over furniture as shown. His body also twists counterclockwise when bumped and clockwise on the desk. (00:09:00)
Other mistake: Cotton's opening line in the movie is that he won't go below 1 million bucks as he's risking his reputation for the cameo, furious that they can't write him a decent part for the Stab movie. So he's still negotiating, but the news story later in the movie says he filmed the cameo the day before.
Other mistake: June 28 was a Monday in 1999. Jenny McCarthy was killed the day before, so on a Sunday. The scene takes places the evening (there's sunlight when it begins) after the night scene with Sidney; it is however uncertain if it is actually supposed to be the same day, or the day before, a Saturday. Therefore, Cotton, murdered a day earlier, was killed on either a Friday or a Saturday, but when he was killed there was a promo on TV about "tomorrow's" episode of his talk show, which is on during weekdays and so wouldn't be on for the weekend.
Other mistake: You can read the date of the event at Jennifer's house on the fax; it's June 28 1999. However, if you look at the director's office in the scene with Sarah, June was a very light month with according to the post-its mostly scouting for locations and such, and no shoots were scheduled in that month, as opposed to August that is full of those. All the previous scenes at the studio involved the actors on set for their scenes, and the news voiceover says that Cotton shot his cameo role the day he was killed.
Other mistake: Gale arrives at Jennifer's house for the party, rings the doorbell, but inexplicably, nobody answers. Noticed by Wes Craven in the DVD commentary; they said they "got away with it" by not adding the sound effect of the doorbell ringing in post so most people would Miss the gesture. (00:39:00)