This counts BTUs this card received over the internal cell bus that referenced a PVC identifier the card doesn't recognize. Because this error occurs entirely on the chassis-internal bus rather than the external network, a rising count here points to an internal circuit-table inconsistency between cards, for example a PVC deleted on one card while another card in the chassis still has stale internal state referencing it, rather than any external line or customer-facing fault. For example, cardInvalidPvcBTUs climbing right after a PVC is removed from the switch's config suggests another card still holds stale internal cell-bus state referencing that now-deleted circuit.