Hmmm just tried to reproduce your experience. As there is more than one change, and some trips are completely outside Germany, it says 'unknown fares abroad' followed by "The Check of the offer and the fare will take place in the service center". So I think what they mean here is give us your £ and we'll do the booking for you, at whatever it costs for the bits we can't price online.
The trip I found (arbitrary date in September) was this one:
Hoek van Holland Haven Th, 17.09.09 dep 09:37
Rotterdam Centraal Th, 17.09.09 arr 10:08
Amersfoort Th, 17.09.09 arr 11:15
Osnabrück Hbf Th, 17.09.09 arr 14:06
Hamburg Hbf Th, 17.09.09 arr 16:12
The problem here seems to be that the bit inside the Netherlands can't be priced by DB. IIRC when I booked I left inter-Netherlands travel to buy on the day fares as there didn't seem to be any savings fares about, and you couldn't book more than a month in advance anyway.
If you tried to split the journey, and buy separate tickets, you could have bought the Amersfoort -> Hamburg leg (above) 'from' €39 single (and fares still available at that rate as at now) and bought the Hook of Holland -> Amersfoort leg from ns.nl for €15.80 single (which as I said IIRC is standard fare).
Like most things, train pricing never seems to work if you want to go from A to B and it involves a change. I've tried to book a ticket before to get to Edinburgh, and if I booked from city centre to city centre I could get the 'advance' tickets at a reasonable price. But add on the bit to get from city centre to suburb (never more than £2 walkup on the day...) and the price trebled.
Better luck next time...?
If you want to speak to an English person about the fares, you might give this a shot
(
http://www.bahn.de/db_uk/view/index.shtml) although they might not be able to help, and of course it's one of those lovely 0870 numbers.