Unable to load boot.ipxe - Please help!

[NiKiZe]

Please check that the ipxe file actually starts with !#ipxe and does not have any BOM chars in the begining.
You can test by using imgfetch http://10.10.10.10/iPXE/boot.ipxe
then imgstat which should show as script, if it says NBP instead you have an issue with the script.

If that does not resolve the issue, read on...

When you have issues what does your http log says?

What is the pciid of your nic? (you can run config in ipxe to show lots of settings, the netX/busid is what I'm after to know which nic you are using)
Have you tested on multiple machines?