Divinity will not set up if the weather is humid or it is raining. Never make it on a humid day.
One thing that might cause it is to not beat it long enough...or perhaps you didn't drizzle the syrup slowly enough into the egg whites. Also, I recommend using a candy thermometer instead of relying on the "cold water" method that was used years ago. On occasion, I, too have had a batch that doesn't want to set up. I usually "fix" it by adding powdered sugar to the recipe until it will hold its shape and then spoon it out as usual.
Harlean from Arkansas
One year I had the same problem and I did a very stupid thing and I threw the fudge in the garbage. Since your fudge didn't set up, don't throw it away but use the fudge as frosting. Bake a batch of chocolate brownies and frost them.
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