Just to let you know. It wasn't possible to purchase the flight online. As stated here before (thanks andrewwm) the false SK inventory was the reason. Spent 1 hour on the phone to solve this issue. Maybe I got too nervous I still could hold the reservation for a longer time. They honored the Farelock eventhough there was no K class more available. I got CPH-FRA-SFO-KOA in V class instead of K class for the same price! I think this is a good news as the regular price right now for this combination is about 400 Eur more then I paid!