I can reproduce this but I don't have a solution right now.

@Eurail Community Moderator, is there a general problem with Renfe trains? Madrid-Barcelona results in the same error.

​@Eurail Community Moderator 

Any idea what the problem is? Booking Spanish trains still doesn't work:

Hi ​@Cesar Henriquez & ​@rvdborgt, apologize for the problem. We had some technical issue with the booking system and fortunately it was already fixed yesterday afternoon. We can reproduce the reservation availability for both connections

​@Cesar Henriquez  if you still find any issue with the error page, please contact our customer support. We hope it helps!