ID:176684 Unable to place CK/CKn pair <name> and <name> on a differential pin pair because they have been assigned to incompatible pins not belonging in the same pair

CAUSE: You have made a pin location assignment on the CK and CKn pin to pins not belonging to the same differential pin pair. Because of this assignment, the CK and CKn pin cannot be placed on a differential pin pair.

ACTION: Remove the pin location assignments or change the pin location assignments to a differential pins in the same pair.