ID:176682 Unable to place CK/CKn pair <name> and <name> on a differential pin pair because <name> has been assigned to a non-differential pin

CAUSE: You have made a pin location assignment on the CK/CKn pin to a non-differential pin. Because of this assignment, the CK and CKn pin cannot be placed on a differential pin pair.

ACTION: Remove the pin location assignment or change the pin location assignment to a differential pin.