If you’re Running Ubuntu, or Debian you can try the DNSMASQ service, it sometimes helps to alleviate issues and resolve to your tftp boot server with your correct file.
Instructions can be found here: [url]http://www.fogproject.org/wiki/index.php/Using_FOG_with_an_unmodifiable_DHCP_server/_Using_FOG_with_no_DHCP_server#DNSMASQ_settings_for_iPXE[/url]
Use the section DNSMASQ Settings for iPXE.