This thread seems close to my problem - I have a non stick griddle that chicken with a marinade was cooked on. The griddle was brand new, and was washed and prepped according to the instructions that came with it. The surface is now coated with black gunk that will not come off. I soaked it in hot water overnight twice, have used a wide variety of scrub pads, from non-abrasive up to a mild abrasive (had to get progressively tougher) and then brought it back to the store. They were willing to take it back, but suggested trying a product called Bar Keepers Friend, which while abrasive, they said would not harm the surface. Since they will still take it back, I figured I would try cleaning it some more and even tried a portable steamer - still no luck.
This is a reputable (as far as I know) brand from a reputable chain, and I'm just amazed that cooking chicken on a griddle would render it useless after one use. I've owned many a non-stick surface and never had this problem before. Just wondering if anyone has had similar experiences.