Here follows an alternative way for resetting the display preferences:
1. Remove the DisplayLink adapter
2. Boot in safe mode (pressing and holding the shift key after the startup tone,
http://support.apple.com/kb/HT1455)
3. Just open the Display preferences in system preferences (not sure this is needed)
4. Reboot
5. Connect your DisplayLink adapter. The rotation should be back to standard.
Hope to have good news soon.