This Counter counts cells transmitted by the BNM Cell Bus Master to the cell bus for which no acknowledgement was received, meaning the intended slave card was missing or inactive. A nonzero and growing value directly indicates cells are being sent toward a card slot that isn't responding, which points to a missing, failed, or misconfigured target card. An admin seeing this counter climb would check whether the destination card for this BNM's cell-bus traffic is actually seated and operational in its slot.