I'm booked on LH492 FRA --> YVR tomorrow (April 4th) in Premium Economy. Booked this flight about 2 weeks ago, and at that time the Lufthansa website told me I couldn't reserve a seat (and to wait for online checkin 23 hours prior to departure). So I wait...until today...23 hours before departure, and now I'm getting a "seat assignment is not possible". I called Lufthansa and all the Agent could do for me was to confirm my booking (and I am confirmed on the flight). Other than that, no help whatsoever as to why I'm not able to grab a seat. So what does "seat reservation not possible" mean? Premium Economy oversold perhaps? Something else?

thanks in advance...
Jeff