I got into the same problem after installation of Debian Stretch, that
is currently in RC stage.
I applied settings from well-running Debian Jessie system. Everything
works, except NBD. I got the same symptoms, and in /var/log/syslog I read:
Negotiation failed/8a: Requested export not found, or
I'm running debian testing on my LTSP server and have just applied the
upgrades. It was working before the upgrades.
I upgraded the server with
sudo apt update
sudo apt upgrade
Then I upgraded the fat client
sudo ltsp-chroot -m
sudo apt update
sudo apt upgrade
exit
sudo ltsp-update-image
sudo
