package supervisor 3.0a8-1.1 failed to install/upgrade: subprocess installed post-installation script returned error exit status 2

[Leonardo Santagada]

maybe the problems is that I have setuptools installed:

Processing triggers for python-support ...
Errors were encountered while processing:
 supervisor
E: Sub-process /usr/bin/dpkg returned an error code (1)
A package failed to install. Trying to recover:
Setting up supervisor (3.0a8-1.1) ...
Starting supervisor: /usr/bin/supervisord:5: UserWarning: Module supervisor was already imported from None, but /usr/lib/pymodules/python2.7 is being added to sys.path
  from pkg_resources import load_entry_point
Error: No config file found at default paths (/usr/etc/supervisord.conf, /usr/supervisord.conf, supervisord.conf, etc/supervisord.conf, /etc/supervisord.conf); use the -c option to specify a config file at a different path
For help, use /usr/bin/supervisord -h
invoke-rc.d: initscript supervisor, action "start" failed.
dpkg: error processing supervisor (--configure):
 subprocess installed post-installation script returned error exit status 2
Processing triggers for python-support ...
Errors were encountered while processing:
 supervisor

ProblemType: Package
DistroRelease: Ubuntu 12.04
Package: supervisor 3.0a8-1.1
ProcVersionSignature: Ubuntu 3.2.0-23.36-generic 3.2.14
Uname: Linux 3.2.0-23-generic x86_64
ApportVersion: 2.0.1-0ubuntu5
AptOrdering: supervisor: Configure
Architecture: amd64
Date: Thu Apr 19 16:09:47 2012
ErrorMessage: subprocess installed post-installation script returned error exit status 2
InstallationMedia: Ubuntu 12.04 LTS "Precise Pangolin" - Beta amd64 (20120328)
PackageArchitecture: all
SourcePackage: supervisor
Title: package supervisor 3.0a8-1.1 failed to install/upgrade: subprocess installed post-installation script returned error exit status 2
UpgradeStatus: No upgrade log present (probably fresh install)

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Ludovico Cavedon (cavedon)]

The cause of this for me was that supervisor was already installed via pip.
Running
   pip uninstall supervisor
fixed the issue for me.