package ntp 1:4.2.6.p3+dfsg-1ubuntu3 failed to install/upgrade: ErrorMessage: subprocess installed post-installation script returned error exit status 1

[Michael Kadmiel]

unable to install nis ntp files for 12.04

ProblemType: Package
DistroRelease: Ubuntu 12.04
Package: ntp 1:4.2.6.p3+dfsg-1ubuntu3
ProcVersionSignature: Ubuntu 3.2.0-23.36-generic-pae 3.2.14
Uname: Linux 3.2.0-23-generic-pae i686
ApportVersion: 2.0.1-0ubuntu6
Architecture: i386
Date: Mon Apr 23 14:33:11 2012
ErrorMessage: ErrorMessage: subprocess installed post-installation script returned error exit status 1
InstallationMedia: Ubuntu 11.04 "Natty Narwhal" - Release i386 (20110426)
NtpStatus:
 remote refid st t when poll reach delay offset jitter
 ==============================================================================
 *london.me-corp. 128.139.6.30 2 u 28 64 17 0.334 1.498 1.101
ProcCmdline: BOOT_IMAGE=/boot/vmlinuz-3.2.0-23-generic-pae root=UUID=9fddc956-cf12-438e-852b-96edf520fb2c ro splash vt.handoff=7
SourcePackage: ntp
Title: package ntp 1:4.2.6.p3+dfsg-1ubuntu3 failed to install/upgrade: ErrorMessage: subprocess installed post-installation script returned error exit status 1
UpgradeStatus: Upgraded to precise on 2012-04-23 (0 days ago)
modified.conffile..etc.ntp.conf: [modified]
mtime.conffile..etc.ntp.conf: 2012-03-27T10:48:18

[James Page (james-page)]

Setting up ntp (1:4.2.6.p3+dfsg-1ubuntu3) ...
Installing new version of config file /etc/apparmor.d/usr.sbin.ntpd ...
chown: invalid group: `ntp:ntp'
dpkg: error processing ntp (--configure):
 subprocess installed post-installation script returned error exit status 1