One of mTurks newest improvements is a new message for when you are unable to accept a HIT. There are no HITs in this group available to you at the moment. (Why?) There are no more HITs available to Workers for this HIT group. You have accepted each HIT in the group. Each HIT has been submitted, returned, or has expired. All the HITs in the HIT group have been accepted by Workers. The HIT group is experiencing extremely high demand and is not available to new Workers at the moment. The newest thing on this list is "The HIT group is experiencing extremely high demand and is not available to new Workers at the moment.", and this is what we refer to as batch throttling. You will notice this with popular batches such as the Ibotta - Are these receipts the same? HITs. This means that there are too many people trying to accept the HITs from the batch, and mTurk now limits the amount of people per batch (number unknown), so you were denied and booted to the no HITs available message. The only thing you can do is try again to accept the HIT again.