Deck Coordinator (Supervisor) dislocated shoulder while climbing down from a third party filter press. The operation was to offload a two-section filter press from the workboat and to stack-up the filter press on the rig. After the base of the filter press was landed on the rig, two Roustabouts put on their fall protection equipment and climbed seven (7) feet to the top of the filter press to pin the fold-down handrails in place. The handrails had to be erected before the top section could be landed on the base. One Roustabout climbed down from the aft end of the unit using the rungs of the protective cage, while the Deck Coordinator climbed down from the unit using the filter support beams. When the Deck Coordinator stepped on the sub-rack, which was approximately two (2) feet from the deck, his foot slipped. As he fell backwards he grabbed the filter support beam to arrest the fall and dislocated his shoulder.