Hi guys,
I had this and tried reinstalling the drivers etc with no luck. In the ethernet settings there was no MAC address. I manually added one and it worked.
This is for a corporate Win 7 x64 image, the Dell OEM worked. There was a driver not included in the Dell service tag downloads which was on the link:
http://www.displaylink.com/support/ticket.php?id=315
(Intel USB 3.0 for Dell Latitude XPS)
This seemed to fix the problem. Dell needs to add this to their download page!