Problem with postgresql-common

[Andrew Punch <andrewpunch@emporiumbooks.com.au>]

Hi,

I am trying to use backports.org for the first time, in order to install 
postgresql 8.1

However the installation falls over at the postgresql-common package 
with the error:
dpkg: error processing 
/var/cache/apt/archives/postgresql-common_57bpo1_all.deb(--unpack):
subprocess pre-installation script returned error exit status 1
Errors were encountered while processing:
/var/cache/apt/archives/postgresql-common_57bpo1_all.deb
E: Sub-process /usr/bin/dpkg returned an error code (1)


I searched the backport.org mailing list archives and Google groups with 
no success. I found a few bugs that seemed loosley related, eg:
http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=351490


If anyone knows any workarounds for this I would appreciate it.


My system is Debian stable 3.1r0. My sources.list file is as follows:
# deb file:///cdrom/ sarge main

# deb cdrom:[Debian GNU/Linux 3.1 r0a _Sarge_ - Official i386 Binary-3 
(20050607)]/ unstable contrib main
# deb cdrom:[Debian GNU/Linux 3.1 r0a _Sarge_ - Official i386 Binary-2 
(20050607)]/ unstable contrib main
# deb cdrom:[Debian GNU/Linux 3.1 r0a _Sarge_ - Official i386 Binary-1 
(20050607)]/ unstable contrib main


deb http://ftp.wa.au.debian.org/debian/ stable main
# deb http://ftp.au.debian.org/debian/ stable main
deb-src http://ftp.au.debian.org/debian/ stable main

deb http://security.debian.org/ stable/updates main contrib
deb http://www.backports.org/debian/ sarge-backports main contrib non-free

#deb http://download.videolan.org/pub/videolan/debian sarge main

Thanks
-Andrew