This counts BTUs received over the cell bus that arrived with detected errors. A rising count here specifically implicates the backplane or cell-bus path to this card, such as connector seating or the card's own bus interface chip, rather than anything on the external network side, since these errors occur entirely inside the chassis. For example, cardInErrorBtus climbing steadily after a chassis was moved suggests the card may have been jostled loose from its backplane connector during the move.