package python-bzrlib 2.6.0+bzr6593-1ubuntu1 failed to install/upgrade: ErrorMessage: subprocess installed post-installation script returned error exit status 101

Apport gave this error during a release upgrade to 14.04 from 13.10. Release upgrade completion failed (no cleanup). Still, dpkg lists this package as installed (ii) so we don't really know what happened here.

ProblemType: Package
DistroRelease: Ubuntu 14.04
Package: python-bzrlib 2.6.0+bzr6593-1ubuntu1
ProcVersionSignature: Ubuntu 3.13.0-24.46-generic 3.13.9
Uname: Linux 3.13.0-24-generic x86_64
NonfreeKernelModules: nvidia
ApportVersion: 2.14.1-0ubuntu3
Architecture: amd64
Date: Thu May 1 13:56:02 2014
DuplicateSignature: package:python-bzrlib:2.6.0+bzr6593-1ubuntu1:ErrorMessage: subprocess installed post-installation script returned error exit status 101
ErrorMessage: ErrorMessage: subprocess installed post-installation script returned error exit status 101
InstallationDate: Installed on 2011-04-29 (1097 days ago)
InstallationMedia: Ubuntu 11.04 "Natty Narwhal" - Release amd64 (20110427.1)
SourcePackage: bzr
Title: package python-bzrlib 2.6.0+bzr6593-1ubuntu1 failed to install/upgrade: ErrorMessage: subprocess installed post-installation script returned error exit status 101
UpgradeStatus: Upgraded to trusty on 2014-05-01 (0 days ago)