Well one thing that might have happened installing Parallels 6 is that the DL device is being hijacked and connected to the virtual machine instead of the Mac. You'll need to check the Parallels settings about the USB devices.
It may also be something wrong with our SW but I'd need the logs to cofirm this, would be great to collect them just after having logged in.
You can use this tool
http://www.displaylink.com/support/ticket.php?id=269 and the attach them here or open a support ticket on our website.