package calendarserver 2.4.dfsg-6 failed to install/upgrade: subprocess installed post-installation script returned error exit status 1

[C-x-s]

Binary package hint: calendarserver

Release: 11.04
---
calendarserver:
  Installed: 2.4.dfsg-6
  Candidate: 2.4.dfsg-6
  Version table:
 *** 2.4.dfsg-6 0
        500 http://de.archive.ubuntu.com/ubuntu/ natty/universe i386 Packages
        100 /var/lib/dpkg/status
---
expected behavior: it should install properly
---
actual behavior: installation failed

ProblemType: Package
DistroRelease: Ubuntu 11.04
Package: calendarserver 2.4.dfsg-6
ProcVersionSignature: Ubuntu 2.6.38-8.42-generic-pae 2.6.38.2
Uname: Linux 2.6.38-8-generic-pae i686
NonfreeKernelModules: nvidia wl
AptOrdering:
 calendarserver: Install
 calendarserver: Configure
Architecture: i386
Date: Tue May 3 07:58:50 2011
ErrorMessage: subprocess installed post-installation script returned error exit status 1
PackageArchitecture: all
SourcePackage: calendarserver
Title: package calendarserver 2.4.dfsg-6 failed to install/upgrade: subprocess installed post-installation script returned error exit status 1
UpgradeStatus: Upgraded to natty on 2011-05-02 (0 days ago)