package libgtk2.0-cil 2.12.10-1ubuntu1 failed to install/upgrade: ErrorMessage: subprocess installed post-installation script returned error exit status 9

[Michael Taylor]

Binary package hint: gtk-sharp2

thought i had upgraded to 11.04 the other day so was surprised when Ubuntu asked me if i wanted to upgrade to 11.04.
According to system info:
You are using Ubuntu 11.04 - the Natty Narwhal - released in April 2011 and supported until October 2012.

ProblemType: Package
DistroRelease: Ubuntu 11.04
Package: libgtk2.0-cil 2.12.10-1ubuntu1
ProcVersionSignature: Ubuntu 2.6.35-28.50-generic 2.6.35.11
Uname: Linux 2.6.35-28-generic i686
NonfreeKernelModules: nvidia
Architecture: i386
Date: Thu May 12 16:48:36 2011
ErrorMessage: ErrorMessage: subprocess installed post-installation script returned error exit status 9
InstallationMedia: Ubuntu 10.04.1 LTS "Lucid Lynx" - Release i386 (20100816.1)
SourcePackage: gtk-sharp2
Title: package libgtk2.0-cil 2.12.10-1ubuntu1 failed to install/upgrade: ErrorMessage: subprocess installed post-installation script returned error exit status 9
UpgradeStatus: Upgraded to natty on 2011-05-12 (0 days ago)