issue with pygrub and xen418

[Mark Davies <mark%ecs.vuw.ac.nz@localhost>]

I just switched one of my xen dom0 boxes from xen 415 to xen 418 and an 
archlinux client that was booting now fails with:

Parsing config from /etc/xen/barretts
libxl: error: libxl_bootloader.c:455:libxl__bootloader_run: Domain 
7:failed to create bootloader dir /var/lib/xen/bootloader.7.d: No such 
file or directory
libxl: error: libxl_create.c:1653:domcreate_rebuild_done: Domain 
7:cannot (re-)build domain: -3
libxl: error: libxl_domain.c:354:libxl_domain_info: Domain 7:Getting 
domain info: No such process
libxl: error: libxl_domain.c:1179:libxl__destroy_domid: Domain 
7:Non-existant domain
libxl: error: libxl_domain.c:1133:domain_destroy_callback: Domain 
7:Unable to destroy guest
libxl: error: libxl_domain.c:1060:domain_destroy_cb: Domain 
7:Destruction of domain failed


/etc/xen/barretts is:

bootloader = "/usr/pkg/bin/pygrub"
memory = 16384
name = "barretts"
    [...]


If I change it to:

kernel = "/xen/arch.run/vmlinuz-linux"
ramdisk = "/xen/arch.run/initramfs-linux.img"
extra = "root=UUID=cbd55299-1517-4995-a70e-ae6db4361c3d"
memory = 16384
name = "barretts"
     [...]


then it works, but why does pygrub no longer work?

cheers
mark