It looks like this is the same recipe I have from a Bon Appetite magazine.
It does say to let the carmel refrigerate until cold (at least 4 hours or up to 1 day). Then you beat all the frosting ingredients together -
4- 8 oz pkg cream cheese
1 stick unsalted butter
1-1/4 c powdered sugar (10X)
1-1/2 tsp vanilla
1 cup carmel
Did you refrigerate the caramel??? If not- maybe that is the answer-- if you did.....I'm at a loss - I have not made this recipe yet but looks great.
Let me know.