Python-setuptools claims to be installed, but can't import in python (package python-setuptools 0.6.15-1ubuntu1 failed to install/upgrade: subprocess installed post-installation script returned error exit status 1)

I've been trying to install various python packages which require python-setuptools to install themselves, but their installs fail with an early message of "Could not import 'setuptools', falling back to 'distutils'.".

I have setuptools installed, but if I try to reinstall it I get:
Reading package lists... Done
Building dependency tree
Reading state information... Done
python-setuptools is already the newest version.
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
4 not fully installed or removed.
After this operation, 0 B of additional disk space will be used.

Description: Ubuntu 11.04
Release: 11.04

python:
  Installed: 2.7.1-0ubuntu5
  Candidate: 2.7.1-0ubuntu5
  Version table:
 *** 2.7.1-0ubuntu5 0
        500 http://gb.archive.ubuntu.com/ubuntu/ natty/main amd64 Packages
        100 /var/lib/dpkg/status

ProblemType: Package
DistroRelease: Ubuntu 11.04
Package: python-setuptools 0.6.15-1ubuntu1
ProcVersionSignature: Ubuntu 2.6.38-13.53-generic 2.6.38.8
Uname: Linux 2.6.38-13-generic x86_64
AptOrdering:
 python-lxml: Configure
 python-pygments: Configure
 python-setuptools: Configure
 python-sphinx: Configure
Architecture: amd64
Date: Tue Jan 10 10:47:42 2012
ErrorMessage: subprocess installed post-installation script returned error exit status 1
InstallationMedia: Ubuntu 11.04 "Natty Narwhal" - Release amd64 (20110427.1)
PackageArchitecture: all
SourcePackage: distribute
Title: package python-setuptools 0.6.15-1ubuntu1 failed to install/upgrade: subprocess installed post-installation script returned error exit status 1
UpgradeStatus: No upgrade log present (probably fresh install)