package ruby1.8 1.8.7.352-2ubuntu1 failed to install/upgrade: subprocess installed post-installation script returned error exit status 2

i think the problem is ruby.

ProblemType: Package
DistroRelease: Ubuntu 12.04
Package: ruby1.8 1.8.7.352-2ubuntu1
ProcVersionSignature: Ubuntu 3.2.0-24.37-generic 3.2.14
Uname: Linux 3.2.0-24-generic x86_64
ApportVersion: 2.0.1-0ubuntu7
Architecture: amd64
Date: Tue May 22 09:21:44 2012
DuplicateSignature:
 Setting up ruby1.8 (1.8.7.352-2ubuntu1) ...
 update-alternatives: error: alternative ri can't be slave of ruby: it is a master alternative.
 dpkg: error processing ruby1.8 (--configure):
  subprocess installed post-installation script returned error exit status 2
ErrorMessage: subprocess installed post-installation script returned error exit status 2
SourcePackage: ruby1.8
Title: package ruby1.8 1.8.7.352-2ubuntu1 failed to install/upgrade: subprocess installed post-installation script returned error exit status 2
UpgradeStatus: Upgraded to precise on 2012-05-01 (20 days ago)