I was getting the OP’s error. When trying to mount the NFS it was failing. I noticed that it had the wrong IP address, it was that of the outside NAT card, no the internal LAN card (VM). After correcting the settings in the FOG server (Storage management, all stoage nodes, edit, IP Address) I was still seeing that incorrect IP address when booting a host. I tried rebooting the server thinking that something might not have applied correctly - no difference.
Then I decided to try registering the host again through the boot menu. After that and setting up the image task it was able to start the task! I don’t know if the settings are actually stored on the host machine or if it’s just coded into the host configuration file, but I would suggest that to everyone having problems in this thread. Make your changes, re-register your client, and then see if it works for you.