Ice Cream/Sherbert making troubles

Hi, just joined chowhound today and I`m excited to be in this awesome community :). So I just started making ice cream for the first time, and I'm using a recipe based on David Lebovitz's Chocolate Sherbert (It`s on his website). I used all the ingredients except the alcoholic ones. So I put the mixture in Ice Cream maker (Rival IC-500). After 25 minutes the consistency was just the same as before, there were no changes apart from the fact it was cooler than before. I made sure the base was chilled overnight in the refrigerator (approx 20 hours) and the canister was in the freezer for a good few days.
Is there anything I'm doing wrong or is it just my ice cream maker?
Help would be greatly appreciated!