Is there a ring that sticks to the bottle? Can you describe how you cleaned and sanitized your bottles? Does it appear in all bottles, or just a portion of the bottles?
That sort of thing is most often mold from poor bottle cleaning. Open a bottle and see if the beer is soured or smells funny. If the beer seems OK, that is just mold and you can actually pick it out and still drink the beer. If you don't have all the beers in the fridge, definitely get as many as you can down to serving temps, that'll stop the growth of both mold or any beer-infecting bacteria.