Problem reservation seat ''prices unavailable'' on all routes

Hello to all,

I have problems to book different trains on the interrail website.

For example, I'm planning to travel from Berlin to Gdansk on July 31st. When I enter the information on the website, I can't make a reservation. It is marked on all the routes: 

Prices unavailable
No fares were found for this route. Passholder seats may be sold out. Search for another route or see "More Information" for other booking options. If Pass seats are sold out, you will need to purchase a full-fare ticket for this route.

I should point out that I could normally book them as they can be booked two months in advance.

What should I do?

Thank you for your help.