Have a look here:
http://forum.ebox-platform.com/index.php?topic=2360.msg10138#msg10138Easiest fix is simply to upload a boot image.
http://rom-o-matic.net/gpxe/gpxe-1.0.1/contrib/rom-o-matic/Choose "PXE bootstrap loader keep [Keep PXE stack method 1] (.kpxe)" and "all-drivers" then click Get Image.
Upload the resulting file to ebox's DHCP under Advanced Options -> Thin Client, choose Next Server: eBox, then click browse and upload the gpxe-1.0.1-gpxe.kpxe file.
That should take care of your test -f warnings, because now the file should exist.
It's not fatal or anything; but should probably be filed as a bug and fixed at some point.
Also -- you can't make changes to the dhcpd.conf directly; eBox will overwrite them from it's template every time you save the module. You *can* however, edit the template, with the caveat of losing your changes each time the module's upgraded. They live in /usr/share/ebox/templates/