When the machine boots does it pull the pxe menu, or does it error out and continue booting to the OS?
In the past with certain revisions of Ubuntu, we had to doctor some services to start on each reboot. I would not be surprised to find that a service was not started properly on boot.
Start by verifying that the apache and tftp services are running.
[code]sudo service apache2 restart
sudo service tftpd-hpa restart[/code]
Try to navigate to the fog management UI, did the web page display? Pxe boot a machine, does the menu appear? can you register the machine to the fog server?