Thank you for your reply.
I have tried rebooting the device repeatedly, as suggested on another thread, and for some reason I seem to have it working now!
I feel that it might have had something to do with the way that I was putting the CF card into the device. I note that it needs to be quite firmly pushed into the slot and I have reached the conclusion that perhaps I was not placing it in properly.
Anyway, the good thing is I have it working now.