Place watermelon cubes in a blender container or food processor bowl.
Cover and blend or process till smooth. (There should be 3 cups of the mixture.)
Stir in sugar.
In a small saucepan combine gelatin and cranberry juice cocktail.
Let stand for 5 minutes.
Stir mixture over low heat till gelatin is dissolved.
Stir the gelatin mixture into the melon mixture.
Pour into an 8x8x2 inch baking pan.
Cover and freeze for 2 hours or till firm.
Break up frozen mixture and place in a chilled mixer bowl.
Beat with an electric mixer on medium to high speed or till mixture is fluffy.
Return to pan.
Cover and freeze for 6 hours or till firm.