Is the bolt a Campy bolt? The Campy bolt is serrated on the female end to prevent it from turning from the turning force of the male bolt. You should be able to remove it by partially threading the male bolt in and then giving the male bolt a sharp whack with a brass or soft faced hammer. As for the bolt not tightening enough to hold the seat post, check to make sure the shoulder of the male bolt isn't bottoming out on the female bolt. If it is, buy a shorter bolt,(Campy makes two different lengths I think) or file or Dremel a couple millimeters of the female bolt. Hope this helps.