The best is to call SNCF (press #85 for English, only American Express accepted from outside of Europe) or call NS (also Visa and Mastercard). No booking fees, reservations will be sent via e-mail.

We suffered a brief technical glitch around this time which prevented travelers to continue to checkout. Thankfully this has since been resolved. Should a similar problem ever occur in the future, you can either make a reservation locally at the station or use the alternative reservation methods. From travel to/from/within France you can either call SNCF +33 1 84 94 3635 (press #85 for assistance in English).

Just reserved two first class seats on an ICE from Paris to Karlsruhe using my Interrail Global Pass. Seat reservations are compulsory on this leg of our journey but the seats allocated via the Interrail reservation system are totally unacceptable. Although they are consecutively numbered they are on a single row so travelling one behind the other. On contacting the booking service I was told that the rail company allocate the seats and so they cannot help. Do any fellow experienced rail travellers have potential solutions?

Many thanks.

Reserving it via  Bahn.com. Fill out your travel details for your route, the amount of passengers and then click "seats only".

For all other alternative seat booking (which usually means booking direct at the operator - often making you choose seats), check this page: 

That doesn't work for trains with mandatory reservations. Nor does DB offer to choose seats for Paris - Karlsruhe. What might work is to call SNCF. That is, if there are still 2 seats available next to each other.