Maybe it's better to remove this directory in the prerm script of fai-quickstart. Would this help? IMO the problem is, that fai-server (which includes nfsroot.conf) is removed before fai-quickstart is removed.
-- regards Thomas -- To UNSUBSCRIBE, email to debian-bugs-dist-requ...@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org