Pots have a wattage rate. They are resistors after all. Generally their resistance is high enough that you can wire the two ends of them between the positive and negative rail without problems, using the wiper to pick up the reference voltage that will be read by the microcontroller. But if you wire one end of the potentiometer to the a voltage rail and the wiper to the other, when the wiper is turned so that the resistance between the two pins is very small the potentiometer will allow too much current through and let out the magic smoke. This can also happen if the microcontroller allows too much current through its ADC pin, but that's VERY unlikely.
Can you tell us the specifications of the pots you are using? Maybe they are not even pots, not everything with a knob on is.
Last edited by Brandano; 09/26/14 12:43 PM.