In a small saucepan, bring 250 mL (1 cup) of Allen’s Cranberry cocktail and sugar to a boil. Stir until sugar is completely dissolved. Remove from heat.
Add remaining cranberry cocktail (750 mL/3 cups).
In a large airtight container, combine sweetened cranberry cocktail, vodka, triple sec and lime juice. Cover. Freeze for about 8 hours or until mixture is firm.
In a food processor, puree frozen mixture until smooth or scrape surface with a fork and break up into crystals. Spoon slush into glasses.
Store the rest in the freezer in an airtight container.