Continuity mistake: When the dwarves find the invisible barrier, Wally takes the map from Randall and calls him crazy. Randall then picks up a skull and throws it, shattering the invisible barrier. At this point Randall takes the map back from Wally, then the camera angle changes and we see Randall taking the map off Wally again.
Continuity mistake: Near the end of the film, there's a scene where the bandits are trapped in a cage hanging from a huge rope. One of the bandits crawls up on top, and severs multiple strands about 4' in length from the rope, leaving the cage hanging from a tiny strand. A bit later, when the cage is being swung back and forth, the missing section of rope has shortened considerably.
Continuity mistake: When Wally has jumped off the bottom of the cage and caught the rope, the rope holding the bandits' original cage snaps. This original cage (which has Wally's rope firmly tied to it) falls into the abyss. When the other bandits pull Wally up, there is no sign of the cage, which should have also shown up. Also, Wally is hanging on at the end of the rope, but he was in the middle of it before the cage's rope snaps.
Continuity mistake: In the "hanging cages" scene, when the rope holding the first cage finally breaks and the cage drops, the only thing holding the other end is one of the characters, who was shown earlier with the rope around his chest and holding on by his fingers. He should have been pulled into the abyss when all the slack was gone.