can't open '/conf/arch.conf'

[NiKiZe]

You don't give much to work with,
It would be good to know which binary you are using,
also good if you posted the script you where using to get this.

With the information at hand my guess would be that you are booting in EFI mode, and are missing initrd= on the kernel line.
This is covered in the FAQ and other recent topics, for example http://forum.ipxe.org/showthread.php?tid=17447

If you are not using EFI you will have to provide more information for anyone to be able to help.

I could also guess that your initrd is broken, please run imgstat before boot, and verify the filesize between what ipxe downloaded and what is in the original file. (there have been instances of corrupted files on http server, or something else that returned data, for example a 404 page or similar)