package libpango1.0-0 1.28.3-4ubuntu1 failed to install/upgrade: pre-installation script returned error exit status 1 - rm: cannot remove `/usr/share/doc/libpango1.0-0': Is a directory

[Jean-Baptiste Lallement]

Upgrade of a real system from maverick to natty.
I worked around by replacing the directory with a file (!?) and finished the upgrade manually.

from term.log
=====
Preparing to replace libpango1.0-0 1.28.2-0ubuntu1.1 (using .../libpango1.0-0_1.28.3-4ubuntu1_i386.deb) ...
386.deb) ...
rm: cannot remove `/usr/share/doc/libpango1.0-0': Is a directory
dpkg: error processing /var/cache/apt/archives/libpango1.0-0_1.28.3-4ubuntu1_i386.deb (--unpack):
 subprocess new pre-installation script returned error exit status 1
=====

ProblemType: Package
DistroRelease: Ubuntu 11.04
Package: libpango1.0-0 1.28.3-4ubuntu1
ProcVersionSignature: Ubuntu 2.6.35-27.48-generic 2.6.35.11
Uname: Linux 2.6.35-27-generic i686
Architecture: i386
Date: Tue Mar 15 12:26:33 2011
DpkgTerminalLog:
 Preparing to replace libpango1.0-0 1.28.2-0ubuntu1.1 (using .../libpango1.0-0_1.28.3-4ubuntu1_i386.deb) ...
 rm: cannot remove `/usr/share/doc/libpango1.0-0': Is a directory
 dpkg: error processing /var/cache/apt/archives/libpango1.0-0_1.28.3-4ubuntu1_i386.deb (--unpack):
  subprocess new pre-installation script returned error exit status 1
ErrorMessage: subprocess new pre-installation script returned error exit status 1
SourcePackage: pango1.0
Title: package libpango1.0-0 1.28.3-4ubuntu1 failed to install/upgrade: subprocess new pre-installation script returned error exit status 1
UpgradeStatus: Upgraded to natty on 2011-03-15 (0 days ago)