Sorry about the delay - had problems replying originally then lost the thread.
The problem turned out to be that the Developer Preview was not picking up the wired network adapter in the little docking station in a timely manner. After about an hour (while I was at a meeting) I came back and the wired network was working fine.
On a reboot it again did not pick it up, but triggering a manual rescan from Device Manager fixed the problem.
It looks like build 8130 has fixed the issue.
David Butchart