alx9r - I have seen this issue with exactly that "corruption" in the file....
FYI - for some strange reason, this is the way that LMCE implements the Boot from HDD option when rebooting an MD. If for some reason you chose in the web admin or the UI, either deliberately or accidentally (easy to do) to boot from HDD, it writes that # character in there that causes the PXE boot to fail and thus drop through to HDD boot... if you have a bootable HDD and it is still in the BIOS boot sequence.
Seems a strange way of doing it, but I think it is important to note that generally, just editing that config file isn't enough as it will regenerate that file with the # character (not sure when this is triggered, but I suspect on every reboot, it certainly appeared to be doing this for me), and the simple way around this is to reboot the MD from the web admin, but first specifically choose Net boot in that web page before hitting reboot. This then removes that # and it will boot normally.