Black Tarry Spots

I have a Whirlpool Dishwasher model DU1010XTXB0. A week ago, I noticed spots -black sticky tar like substance - on my dishes and in the inside of my dishwasher. I had to take a brillo pad to the dishes and also to the inside of my dishwasher to clean of the black spots. We do use the Heat Dry. Any ideas?