Some trains have limited seats for pass holders. But often there are alternatives. There could also be another problem.

Which exact train are you trying to book? From where to where on which date and time?

Refund conditions should be in the confirmation mail you received after ordering.

Also: READ the coutry-info, as this is a coöperate offer of some 50+ different railways in 33 countries, some of these do not even offer the possibility to book seats online. PLUs that in many cases (mostly regional trains) one canNOT even reserve, its just board and find seat-or stand.

Note that the countries where most newbees scold on are Spain and France for this matter.

I've got the same problem and I'm not best pleased 

I don't like the lack of transparency on whether the seats for pass holders are fully booked, or if it's just a technical problem. This needs to be more clear! On other train booking websites, it is very clear how many spaces are left. Which is not the case here.

Please invest more in this.

I want to echo the sentiment of the original message, it's frustrating!! 

Eurail connects to multiple reservation systems and unfortunately, some of them just return something like "not possible” when they can't book the reservation requested, although there are many possible causes. Pass holder seats may be sold out but also there may be an internal problem on the reservation system's side. Or the train is just not open yet for reservation.

If you provide details of the train(s) you're trying to book (origin, destination, date, departure time), then maybe people here can provide more information.

I agree that more clarity would be good (such as the number of seats still available) but I don't know if that's information is available. Maybe @Nanja can shed some light on that?

Update!! 

I called SNCF directly who were very helpful. My train to Montpellier was giving the classic "sold out" message on the eurail website. But I called SNCF on +33184943635 and pressed #85 to speak to an English speaker. 

I was able to book my desired train for €20.

I did have to call twice because after a few minutes of holding the call was dropped the first time. The second time was very quick though.

So... Eurail - fix up! And to potential travellers - calling the train company is maybe your best bet, but it can be a bit tricky and patience is needed 

Strange because SNCF stopped to sell reservations online at their own website and even refused since last summer to sell them on the phone. For bookings of french domestic trains you can use b-europe the website of Belgian Rail :)

Well, seat61 suggests they may sometimes still sell them by phone:

Or maybe they reversed their decision or maybe some employees just do what you ask…

The phone number in the screenshot is incorrect by the way, but so is the English page on the SNCF website.

Then that is the explanation: the Eurail website still has an issue with the 20€ reservations after the 10€ reservations have sold out. @Nanja, is a solution already in sight? I see the new reservation tool also still has this problem.

Hi rvdborgt, the fix that was developed did not work as desired, unfortunately. And due to other priorities work on this fix had to be put on hold. 

Maybe they reversed their policy. Another person succeeded in buying Interrail reservations via SNCF's phone service.