Revealing mistake: When the bad guy free-falls from the crane and dies, he is replaced with an obvious dummy.
Revealing mistake: As Barb is going down the rope with the hostage girl in the beginning of the movie, you can tell it's a stunt person as there are no dark roots showing in her hair (a wig?). Before she goes out the window, and again afterwards, she looks like she needs a root touch-up. Also, the young girl Barb rescues is suddenly an older woman.