@t_dashs Right you can do that by typing in the IP address of your fog server. But the root of the problem is that you have at least 1 dhcp server not handing out the complete information. Understand this is an network infrastructure problem not specifically a FOG issue.
If you have a computer loaded with wireshark on the same subnet as the pxe booting computer we might be able to find out which one is wrong. You will want to use a wireshark capture filter of port 67 or port 68 Start the wireshark capture then pxe boot the target computer til you get this error. Stop wireshark from scanning. In the data area you will see a discover package sent from the target computer and one or more OFFER packets. The problem lies in one of these offer packets. Either the next-server or dhcp option 66 is not set on the offending dhcp server.