RazorServer iPXE vmlinuz0 gets "Exec format Error"
I have installed Razor Server and dnsmasq inside a VirtualBox environment following the wiki steps for installation and getting started. My new virtual node boots and gets the DHCP proxy response and gets the bootstrap.ipxe file and then makes the /svc/boot request and gets the #!ipxe script. It then downloads the /svc/repomicrokernel/initrd0.img and /svc/repo/microkernel/vmlinuz0 files but then gets "Could not select: Exec format error ( http://ipxe.org/2e008001)" . I could see all this running tcpdump/wireshark on the razorserver.
I've tried downloading the microkernel again from "http://links.puppetlabs.com/razor-microkernel-latest.tar" and it all seems fine - the checksums are ok.
VirtualBox version is 4.3.26.
Any suggestions for how to debug further or where I might have gone wrong in the setup?