Most likely, it was too much powdered sugar. When you mix it (and it is easier by hand) hold back some of the PS. Depending on the moisture in the air and the moisture in the sugar, it not not take all the sugar to make a smooth, not sticky mass.
You may be able to rescue what you have with a SLIGHT sprinkle of water, and a couple of seconds in the microwave. Watch out, it gets hot fast.
DON'T throw out what you've made!! It's salvagable! (sp?) Add moisture. Even if you start w/a tbl water then knead it and then I like to put water in my hands and rub them together before kneading again. It adds a little moisture at a time. Also try to do it by hand not by KA, as it seems to me that the ka overworks the "dough". I've always used the whole 2lb bag of 10x sugar with no problems. So try to save it. Alot of people can and like to use their ka, but I like using my hands this way I can feel where the kneading really needs to be done. Hope this helps, good luck!!!
add some water and Crisco...then knead very well....what recipe did you use ? 1 bag of Marshmallow and 1 bag of Powdered sugar, 3 T water, 1/2 to 1 tsp. of Glycerine and 1 tsp of Crisco . This is how I make it..never had a failure... 
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