In the part where Jones and Connery are stealing the Mask, you will find this slip-up.

Where Jones is moving her way through the lasers, being careful not to set one off, she actually does set one off.

Look for the part where she is hunched over, and is on all fours. She raises her left leg, as to moving it over the beam. Then she moves her hands and arms right thru one of the beams as she raises her other leg to let it over. You can see the beam was clearly there, by the next shot of Connery looking into the monitor that shows the lasers.