I have had this problem for the AF bookings I have made since december last year. I book through a travel agent (in Italy) and when I access my account on the AF website it does find my booking, however displaying the infamous message (your reservation cannot be completed in this country, please click here if you want to make changes). I actually do not want to make changes, simply to pre-assign seats, so I do "click here", I get redirected to airfrance.co.uk, but even from there I cannot assign seats. I called my travel agent, they have no clue what is happening and claim that they have nothing to do with the UK, however they are at least able to assign seats for me. As a further data point: this happens both before and after the ticket is issued. And it did not happen before the end of last year.
Any idea what is happening ?
many thanks !