Nope. It's not OK, unfortunately. Potassium sorbate is a preservative: it preserves the juice by preventing micro-organisms from growing in it. That includes the yeast that your want to be there to ferment it. From what I've read there's no really good way to get rid of it, but I could be wrong.
You might as well enjoy your juice (hot mulled cider? Popsicles?) and scout around for some untreated cider to ferment. Pasteurized cider is OK, as is cider with ascorbic acid in it (vitamin C), as long as it doesn't also have potassium sorbate or other preservative in it.
Primary: 19 Gallon (Cranberry) Cyser, Home Alone Cranberry Melomel
Secondary: Tenure Forecast Cider, Riotin' Cider, Virgin Cider No. 1
Bottled: pumpkin ale!, brown ale
Drinking: red ale