Even though this thread is a bit stale, I'm having the same issue. Delta Diamond flyer. Flying MSP - JRS via AMS in business class. Should have zero issues, but I get the same "ticket not eligible" error. From reading all of this, it seems like Delta customers are the ones having the issues. My guess is anything booked on 006 ticket stock is getting rejected by the KLM reservation system.
Does anyone know if there is someone we can call?