Comment 4 for bug 472468

Gordon, it appears that your back-end's permissions were changed from what the package is shipping. Can you try resetting them back to 0700 and see if it solves your problem?

As for distributions, whenever they use some sort of hardening tool (in Ubuntu's case, AppArmor), all sorts of things that were not foreseen by the upstream author can happen. Adding insult to injury, those hardening tools depend on forever changing Linux kernel security features, which often results on what used to work no longer working as expected. Sometimes, those kernel changes get introduced at the last minute, which prevents CUPS-PDF maintainers from fixing any pending issue on time for a new Ubuntu release.