I may have read your post too quickly, so if after you confirm the settings according to the wiki page, you still have issues we can debug using a packet capture. If the fog server and the pxe booting computer is on the same subnet, please use this tutorial to capture the best quality pcap. https://forums.fogproject.org/topic/9673/when-dhcp-pxe-booting-process-goes-bad-and-you-have-no-clue
The pcap will show us what the target computer is being told to do.
If your pxe booting compute is on a different subnet then install wireshark on a witness computer (second computer not part of the pxe booting process). Use the wireshark capture filter of port 67 or port 68 to only capture the pxe boot.
Post the pcap to a file share site (like google drive) and either post the link in the thread or IM me the link and I will take a look at what the client is being told.