Preheat oven to 325 degrees F. On a sheet pan spread out the walnuts and toast in the oven for 7 to 9 minutes. Remove from oven and allow to cool.
In a bowl with an electric mixer, cream together the blue cheese and the cream cheese until smooth. Put one tablespoon of the cheese mixture in the palm of one hand and in it roll a grape, shaping the mixture around the grape to coat. Cover the remaining grapes and chill on a sheet pan for 15 minutes. Roll the cheese-coated grapes in the walnut mixture to cover completely and chill for 30 minutes or until coating is firm. Using a sharp knife cut grapes into halves.