That's what I thought (that the ethernet light is supposed to be lit when the dLAN sees another ethernet device)...
I will try ringing the helpline number - I have found one on devolo's site - although it is difficult as I am working when the offices will be open and am therefore not at home!! I will try when I am next off. Their response to email is very slow...
Thanks for your assistance, however, it is appreciated despite the fact that we are still no further. When I find the solution I shall post it so you know should you ever come across the situation again