Even if the air cell is detatched (meaning it moves around) you can still incubate. Just make absolutely sure the egg stays big end up. I know some people incubate eggs on the sides, so if the detatched air cell is on the side of the egg, it could be trouble for the chick.
I think the air bubble is supposed to be fixed at the end of the egg. You know when you hard boil eggs there is always that flat end? That is where the air bubble is supposed to be. Course I have never hatched eggs but planning to this summer so reading all about it.