It is the paper, you are using paper that is outside of the LaserJet 4200 specifications. HP warns against using paper that thick and notes "…do not use paper heavier than 200 g/m2 (53 lb) in Tray 1 or 120 g/m2 (32 lb) in other trays. Paper that is too heavy might cause misfeeds, stacking problems, jams,
poor toner fusing, poor print quality, or excessive mechanical wear."
Here are the supported paper types from HP
http://h20565.www2.hp.com/portal/si...e.cachetokendon