An employee was working with a crew to lift a gang form with a forklift/tractor over an existing portion of gang form. The employee was on the inside corner of the wall portion of the forms where they were connected on the ground. The tag line caught on the top corner as the form was coming over the existing wall, causing the gang form to rock; the scaffold plank came loose and struck the employee. He fell to the ground, suffering head lacerations, broken ribs, and a possible back injury.