As an aside, these aren't the traditional Congo Bars (which are a version of a Blondie bar) but rather use graham crackers for the base. To make them really extraordinary, try making your own graham crackers to use in this recipe. It really makes all the difference.
Although I haven't made these, I don't think you're doing anything wrong. It would seem that if the caramel recipe is saying to cook it to hard-crack stage and then the popcorn square recipe instructs to bake for 20 minutes that it would be hard as a rock. Perhaps someone from MSL needs to give some advice on this.
Please help! I've tried this recipe unsuccessfully 5 times for the "golden popcorn squares" - it comes out hard as a rock