There still seems to be a distinction in many systems between the old EnRoute cards and Diners Club. At the Marriott where I worked last summer some cards were recorded as EnRoute and some as DC. I'm not sure what the difference was, as they both pretty much look the same. Maybe the issuing country? I take it that the designation would come based on the card number as all we did was swipe the cards and the system would automatically recognize the type. Were the DC cards in question issued in different countries/by different authorities?