Continuity mistake: Gretchen starts talking to that man who doesn't talk, but later when Mikey is singing for the first time, you see that man booing him, then a minute later Gretchen is still talking to him.
Factual error: When Gretchen is typing the pardon on Mrs. Lemon's typewriter, the paper that she is typing on doesn't go up and out of the typewriter gradually as it should. It goes up all at once when she's almost done typing.