I've had the same problem with Targus (what a POS) on my new Dell Ultra Slim laptop. After trying different drivers, trying different ports, plugging and unplugging i gave up and bought a USB 3.0 gigabit adapter and now don't care about the one built into the port replicator. That thing is just buggy despite what the manufacturer claims (read Amazon reviews if you want)
If you want to get done with this quickly - just do what i did and get yourself a USB gig adapter (i got mine here
http://www.usb3gigabit.com/)
A quick update - this is not a problem with display link in any way, there is something wrong with the targus hardware