Unable to make seat reservation from Paris to Zurich

I have a global pass and was able to make a reservation from London to Paris. For Paris - Zurich (June 10th 7.20 am), though it shows seats are available on the eurail website, when I got to checkout, it says one of the legs is unavailable. I saw another post that said reservations were possible only till Basel, so I tried that as well. In fact, I tried removing one station at a time until it was only Paris - Belfort, but even that didnt work. Any suggestions would be helpful.

thanks,

sri