An NYPD sergeant pleaded not guilty Tuesday in court to a manslaughter charges for causing the August death of a Bronx suspect on a scooter by tossing a cooler at him, causing him to crash. Sgt. Erik Duran, 36, entered the plea during his arraignment in Supreme Court in the Bronx. The plea also covered criminally negligent homicide and assault charges which he is also facing for the death of Eric Duprey, 30, on Aug. 23 in Kingsbridge Heights. Duprey, a deliveryman with three young children, was attempting to flee a drug arrest when he crashed. The prosecution is being handled by attorneys with…