Revealing mistake: There are a couple times you can see the tape that marks where the actors are supposed to stand in the shot. In the beginning, when Bobby and his brother walk in on Ernest trying to get a cleaning machine to work, look on the floor and you will see some tape in the shape of a T. Bobby will move his feet to the T. Also when a criminal begs for Nash's help because he killed someone, and Nash walks forward, look on the floor to see another tape T, and what do ya know, Nash stops right on the T.
Continuity mistake: When Ernest pulls the bank banner off the wall and starts flying around, there's shots of that same wall with the banner back up and the two flags are gone.
Revealing mistake: As Ernest is flying around the bank, it can be seen numerous times that he's really sitting in front of a green screen with the bank projected behind him.
Revealing mistake: After Bobby activates the clear barrier, he shoots it to show it's bullet proof. First, he shoots eleven times out of a six-shot pistol. Second, the cylinder never moves. Third, after the shots, you can see there were no rounds in the chambers to start with.