This means that networktablet (or another app using the same port) is already running. You can see a list of running applications and their UDP ports with sudo netstat -an | grep udp.
sudo netstat -an | grep udp
This would be great, for normal tablet users.
I have the same issue, and I have fixed it by
It will also create a /dev/uinput
I have just uploaded the new app version (1.4) to the stores and updated the homepage with a link to the new server.