I think you are fixing a problem the wrong way. The pxelinux.0 is an old boot kernel that should never be used now. If you do use it you WILL get the error you mentioned.
For FOG 1.3.x and beyond you should either use undionly.kpxe for legacy (bios) mode and ipxe.efi for uefi mode. For your setup you need to modify your dhcp server and change dhcp option 67 {boot-file} to undionly.kpxe. While what you did will work its a non-standard setup that may break on the next update to FOG.