Pkg xen devel - Feb 2011 - Bug#603391: pygrub: unintelligible error messages

The image argument to pygrub does not need to be an integer.

The "invalid literal for int()" error probably means that your
menu.lst
contains something like "root=(/dev/sda)". The root should be
specified
in grub notation like "root=(hd0)".

You might want to have a look at /boot/grub/devices.map. To map /dev/sda
to hd0, you could add an entry like:
(hd0) /dev/sda