I 'm trying to book a one way senior (or prems, which I cannot locate) for 2 from Narbonne to Barcelona on the voyages-sncf site on 9/22. Our Barcelona hotel (Le Petit Palace Museum on calle Disutacion near calle Rambla de Catalunya) told me the closest train station is Plaza de Catalunya. When I select that station, the website converts it to Station Francia. So I called Rail Europe and they told me the proper station is Desranca -- not even listed as an option on sncf web!
So 1) how do I navigate to the prems fares? 2) do I need one of the French discount cards to get the senior fare? 3) why do I get vastly different fares each time I look?

Oh Robbie I feel your pain! It took me quite a few attempts before I got it right. The only place I found for SENIOR tickets (which are discounted) is a little 'tick'box you acknowledge while going through the booking process. You can't use the French discount cards - I've read somewhere they are not applicable?!
I do hope someone is going to be able to guide you through it!

Plaça de Catalunya is a station only for metero/regional trains. Station Francia is correct. It's one of the main railway stations in Barcelona. The biggest is Barcelona Sants so you have 2 choices. Desrance, never heard of. Maybe a wrong spelling ?

Irrelevant but "Disutacion" may be Diputation

See the time table (station names) for yourself
http://www.sbb.ch/en/index.htm
(This is a Swiss site but don't ask me why I give it to you for Spanish trains - its reliable and easy to navigate)

You can't usually pick any train station you want to arrive, you have to go where the train goes, which will be limited. Trains from France only go to Barcelona Sants or Franca stations, you can't just go wherever you want. I imagine your hotel is just telling you how you would eventually get there via public transportation, not that they expected you to get a train from France in Plaza de Catalunya. That's a metro station, isn't it? I don't know what Raileurope is talking about.

Trains from Narbonne will go to Sants or Franca stations. YOu don't have to even pick one, I don't know why you are doing that. You just put in Narbonne and Barcelone and it shows you all possibilities of choices, and you can pick the best price/route that way. I just did it, it isn't that complicated, you just put in your cities, the date and check the box for age 60+ and it gives you all ticket possibilites and schedules, including some senior fares (such as at 8:21 and at 16:11 for 32 euro).

As Christina wrote, for checking time table, just put Barcelona and the site I posted above will give you the stations Sants and Francia.

I"m guessing that you're too late for a Prem fare; they are available 3 months out, and on popular routes they go fast. Last week I purchased Strasbourg to Paris on the first day I could for an Oct. date, and there were few Prem seats left.

Your choices for Narbonne-Barcelona are on either Talgo/Corail trains or regional trains. Neither one offers Prem's fares so you won't save any money by booking in advance.

For Corail/Talgo trains your can leave Narbonne at 08:21 and arrive at Barcelona Sants at 11:46. Or you can leave at 16:11 and arrive at Barcelona Franca at 19:59.

The fare for the above routes is 44 EUR.

You can take regional trains with one connection, Narbonne-Port Bou and Port Bou-Barcelona Sants. The fare is cheaper (26.10 EUR), but it's a longer ride.

Oops! I forgot to check for senior fares. As Christina already noted, you can get a senior fare of 32 EUR on either the 08:21 or the 16:11 train.

There are only two direct Talgo trains every day from Narbonne to Barcelona. Seats on these need to be reserved and they are often fully booked in advance. If you want to go on one of these trains, book in good time.
If you're not rushed and want to save money, look up connections at the border station of Portbou. Trains from France to Portbou are irregular. From Portbou to Barcelona, they're generally every hour. For these trains, you just buy a ticket and board the train.

The SNCF website (and SNCF in general) frustrated me for most of my 5 years in France. If you can, get a ticket to the border, then use the Spanish RENFA to get from the border to your destination. That will almost certainly be cheaper and less frustrating.
I have some pages on my website about France and people can choose whether they want to see an optimistic or pessimistic view of France. No prizes for where SNCF appears... Click on
http://www.jeremytaylor.eu/France2.htm if you want to have a look.

Update. I thought I'd finally gotten it right but then found myself in an infinite loupe. I entered all info and pressed the reserve button and a new screen would come on asking for all the info I just provided. After doing this a few times I went to Plan B.
I wrote the owner of the B & B we're staying at just prior to the train trip and asked her for help. What a wonderful feeling to hear that she would go buy the tickets for us. She confirmed next day that she bought them and we can pay her on arrival at Mas de Azemar in Mercues. Not only am I relieved but so pleased at her hospitality and willingness to help. Now I'm reeeely getting excited about the trip.

Good for you, RT.