When you make candy, you are cooking the syrup to the point where you are removing a significant portion of water from that syrup. The point to which you cook it, soft ball, hard ball, hard crack, etc., determines the amount of water you are cooking out of the candy. So, as the candy cools, what you are after is a supersaturated solution of sugar. There is so little water in the solution that it will actually pull water out of the air in an attempt to come to equilibrium (see, you should have paid attention in science class). When all things are optimal, the crystalization process takes place in a very controlled manner. For example, when you make fudge, you cook the ingredients to the soft ball stage, washing down any sugar crystals that might be up on the sides of the pot. WHen the critical temperature is reached, you remove it from the heat and allow it to cool to aboutt 112 degrees F. At that time you add the flavoring, nuts, butter and THEN and ONLY THEN do you stir. This allows the sugar to crystalilze, although making only tiny sugar crystals as it sets. If you mess up and add ingredients or disturb your solution too soon (too hot) the crystalization process has more time, and thus forms larger grains in the fudge (ick). In your case, your candy isn't reaching the correct consistency because your supersaturated solution is pulling water out of the air and forming a gummy concoction rather than the crunchy result you want.
I read in another blog that if you touch your chin to your chest and it feels sticky, then there is too much humidity to make candy. Good luck!