The Rock 'n' Roller Coaster at the Disney-MGM theme park in Florida has been closed for the time being, following the death of a 12-year-old rider. It's the latest in a string of tragedies that have stung Walt Disney World in recent years. Authorities said Michael Russell, of Fort Campbell, Ky., had ridden the Rock 'n' Roller Coaster with his parents and 7-year-old brother. As the family got off the ride, the father noticed his son was limp.