Factual error: In the scene where we first meet Rosie, it opens with a shot of the house and then goes inside, passing by some pictures of Rosie and her husband. One of them, a picture of their wedding, says "Frank and Rosie - Wedding 1948", but then when Rosie is talking about how her husband will know how much she still loves him after all those years, Robbie says that he hopes that he and Linda will be as happy as Rosie and her husband on their 50th anniversary. If they got married in 1948, they would be closer to their 40th wedding anniversary. Since the movie is supposed to take place in 1985, this would actually be their 37th wedding anniversary.
Continuity mistake: At the cake shop for Glen and Julia's Wedding, Adam Sandler is feeding Boy George some samples of cake. First you see 2 pieces of cake on the plate. Then he feeds one to that weird person, and in the next frame with the plate it's empty. Then after that there is still one piece of cake on the plate.
Continuity mistake: When Robbie (Adam Sandler) is lying in the trash dumpster, after he just got dumped, you can see him covered with trash. Then the camera switches to Julia (Drew Barrymore), and when it goes back to Robbie, there's different trash, and less trash, and it isn't in the same position.
Continuity mistake: During the 50th wedding anniversary party, after Rosie is done singing, she walks over to her husband Frank and they embrace with her on the left, and him on the right. The camera cuts away to Adam Sandler, then back to them, only now Frank is on the left and Rosie is on the right. The camera cuts to Adam again, then back to the couple where they are in their original positions.
Continuity mistake: At the first wedding, the left hand side (as we look at it) of the bow tie that the brother of the groom is wearing, keeps appearing and disappearing from his collar.
Other mistake: After the on-board announcement that the plane is at cruising speed and altitude, the exterior shots still show the wing flaps extended for landing. Due to structural limitations and the extra drag created, the flaps cannot be used at higher speeds.
Continuity mistake: At the first wedding he is singing at, the best man comes up and talks, the microphone stand moves into different positions. In one shot it is facing forward and the next it will be backwards. It goes back and forth the whole time.
Continuity mistake: In the first wedding for the Veltrys, George finishes "Do you really want to hurt me" as Julia walks into the kitchen after having her bum pinched. Then the next scene is Robbie telling the drunk boy outside to go in, and in the background is George re-finishing "Do you really want to hurt me". Then George starts the song again as Robbie is not there. The intro is quite long to this song, but then the scene goes back to Robbie outside still helping the boy and the background noise is the middle of "Do you really want to hurt me." This is not possible.
Continuity mistake: When Robbie is singing at his first wedding back (Cindy and Scott's), just after George sings the backup "Holiday", Robbie then sings "It would be.." and when he sings this he lifts his left hand into shot and on his ring finger you can see something white in a ring shape around the top part of that finger, but in the next shot of him after it changes to a shot of the annoyed father and back, the white "ring" that was around his finger is no longer there.
Factual error: Although the movie is set in 1985, the first exterior shot of the airplane shows an A320 (note the winglets) which didn't enter service until 1987.
Continuity mistake: The back ground colour outside the banquet hall keeps changing, in the first scene there is a sign, in the next it's gone.
Continuity mistake: In the scene where Robbie is back at his sisters house talking to his best friend and sister's husband, one of her children (dressed as Freddy) walks up with a picture of Robbie and Linda where he drew on Linda to make her look like the devil. When he hands the picture to Robbie, it is passed to him from the side, but in the next shot a split second later it is passed in front of him (facing frontwards) by the child.