The gpk-service-pack and pkgenpack both not working in Ubuntu. It's error while creating the service pack itself because it can't generate metadata.conf.
After few minutes looking into the source, pk_get_distro_id does not have Debian/Ubuntu's version.
My suggestion is parsing the /etc/lsb-release file, which is in this format:
and in Debian there is also /etc/debian_version, which in my Ubuntu having only 5.0 in that file
Author: Richard Hughes <email@example.com>
Date: Tue May 5 09:55:53 2009 +0100
Add support for /etc/lsb-release to pk_get_distro_id() to fix fd#21550