PostgreSQL installation on Debian: "Sub-process /usr/bin/dpkg returned an error code (1)"

PostgreSQL installation on Debian: "Sub-process /usr/bin/dpkg returned an error code (1)"

apt-get install postgresql
Reading package lists... Done
Building dependency tree      
Reading state information... Done
The following NEW packages will be installed:
  postgresql
0 upgraded, 1 newly installed, 0 to remove and 0 not upgraded.
2 not fully installed or removed.
Need to get 31.8 kB of archives.
After this operation, 65.5 kB of additional disk space will be used.
Get:1 http://http.us.debian.org/debian/ squeeze/main postgresql all 8.4.15-0squeeze1 [31.8 kB]
Fetched 31.8 kB in 1s (22.3 kB/s)    
Selecting previously deselected package postgresql.
(Reading database ... 155014 files and directories currently installed.)
Unpacking postgresql (from .../postgresql_8.4.15-0squeeze1_all.deb) ...
Setting up postgresql-client-8.4 (8.4.17-0squeeze1) ...
.: 5: Can't open /usr/share/postgresql-common/maintscripts-functions
dpkg: error processing postgresql-client-8.4 (--configure):
 subprocess installed post-installation script returned error exit status 127
configured to not write apport reports
configured to not write apport reports
dpkg: dependency problems prevent configuration of postgresql-8.4:
 postgresql-8.4 depends on postgresql-client-8.4; however:
  Package postgresql-client-8.4 is not configured yet.
dpkg: error processing postgresql-8.4 (--configure):
 dependency problems - leaving unconfigured
dpkg: dependency problems prevent configuration of postgresql:
 postgresql depends on postgresql-8.4; however:
  Package postgresql-8.4 is not configured yet.
dpkg: error processing postgresql (--configure):
 dependency problems - leaving unconfigured
configured to not write apport reports

 Errors were encountered while processing:
 postgresql-client-8.4
 postgresql-8.4
 postgresql
E: Sub-process /usr/bin/dpkg returned an error code (1)
I've also tried the following command---
 apt-get -f install
Reading package lists... Done
Building dependency tree      
Reading state information... Done
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
3 not fully installed or removed.
After this operation, 0 B of additional disk space will be used.
Setting up postgresql-client-8.4 (8.4.17-0squeeze1) ...
.: 5: Can't open /usr/share/postgresql-common/maintscripts-functions
dpkg: error processing postgresql-client-8.4 (--configure):
 subprocess installed post-installation script returned error exit status 127
configured to not write apport reports

dpkg: dependency problems prevent configuration of postgresql-8.4:
 postgresql-8.4 depends on postgresql-client-8.4; however:
  Package postgresql-client-8.4 is not configured yet.
dpkg: error processing postgresql-8.4 (--configure):
 dependency problems - leaving unconfigured
dpkg: dependency problems prevent configuration of postgresql:
 postgresql depends on postgresql-8.4; however:
  Package postgresql-8.4 is not configured yet.
configured to not write apport reports

dpkg: error processing postgresql (--configure):
 dependency problems - leaving unconfigured
configured to not write apport reports
                                      Errors were encountered while processing:
 postgresql-client-8.4
 postgresql-8.4
 postgresql
E: Sub-process /usr/bin/dpkg returned