Hi ce119214,
it seems that something went wrong in getting screen updates, but it would help to have some logs from your machine.
Could you please re-install 2.4, connect the DisplayLink device (wait until the secondary screen is visible in system preferences) and gather logs with log tool.
The log tool is at
http://www.displaylink.com/support/ticket.php?id=269
You can attach the logs here or send them through
http://www.displaylink.com/support/ask_question.php
Thanks
Christian