Comment 3 for bug 951526

The problem is that you don't have an /etc/nbd-server/conf.d/ltsp_i386.conf file and so nbd-server doesn't start itself.
That file is generated by ltsp-update-image. So the next information you need to include is any errors that you see after running:

sudo ltsp-update-image
(you might also need: sudo service nbd-server start)

That's supposed to be ran automatically at the end of ltsp-build-client. So if it runs fine for you now, it might mean that ltsp-build-client was interrupted and didn't complete successfully. That in turn might have happened for any number of reasons, even temporary ones like the Ubuntu archive being in an inconsistent state. We'd need the whole ltsp-build-client output to be certain, you probably didn't keep that so if that was the original problem we won't know it until you try ltsp-build-client again.