In the scene when the sergeant and the president are discussing options in the safe room (just before the president shouts shut up!), The sergeant hands the president a clipboard with the nuke paperwork...only problem is that he initially hands it over upside down, yet the next shot shows that it is the correct way up again.
Okay this film was a spoof on the old B-movies and I saw a interview with the director and he said that all these slip ups were done on purpose to make fun of the un-intentional ones in the old films.