I found a work around for this.
I read the post at
http://www.displaylink.org/forum/sho...ghlight=Server in which it mentions :
"My guess is that the primary graphics card or driver you have installed is not a WDDM compatible driver (Windows 7 driver). This is needed by DisplayLink software to operate correctly on Windows Vista and Windows 7 (and their server equivalents)"
After reading this I tried installing the correct Dell Driver for the on board graphics system for the server I am using and then after rebooting it all began working. My guess is that the new/correct driver provided the WDDM interfaces needed by DisplayLink.
In any case it is working now.
Terry Clancy