I called KLM who told me that it is available for all flights and all classes but that it is not working today.

But then the KLM website states 'Selecting your seat

During the booking process, you can indicate where you would prefer to sit. Next to a window or rather on an aisle? We’ll do our best to assign you this seat, whether you make your reservation online, by telephone or with a travel agent.

After you have booked, you can log in at Manage my Booking where you can select the seat you want as early as 90 days before departure. You can also view or change your seat during check-in, at the website or at a self-service check-in machine at the airport.' (http://www.klm.com/travel/nl_en/trav...oard/index.htm)

So maybe it is just not working today? No mention of it just being available for C-class intra-European flights.

Thanks