Remove all unpopped kernels from popped corn. Place popcorn in a disposable greased 17x12x2-inch pan. Keep popcorn warm in 300 oven while making syrup mixture. Butter bottom and sides of heavy 2-qt. saucepan. In the pan combine margarine, sugar, gelatin, water, and corn syrup. Cook mixture over medium heat till boiling, stirring constantly. Clip a candy thermometer to side of pan. Continue cooking over medium heat, stirring constantly, till the thermometer registers 255 (hard-ball stage). Pour syrup mixture evenly over popcorn and shake gently to coat. Bake at 300 for 5 minutes. Shake once more and bake for 5 more minutes. Turn popcorn mixture onto large piece of foil. Cool. Store in airtight container in cool, dry place.