Dselect chown: root.root: invalid group

[Victor <vdemart@supereva.it>]

Trying to unpack devscripts  by means of dselect I've got the following error 
and the package has emained unconfigured:
.............................................................................................................................................................................
(Reading database ... 85443 files and directories currently installed.)
Unpacking devscripts (from .../devel/devscripts_2.5.8.1.deb) ...
Setting up devscripts (2.5.8.1) ...
chown: root.root: invalid group
dpkg: error processing devscripts (--configure):
 subprocess post-installation script returned error exit status 1
Errors were encountered while processing:
 devscripts
E: Sub-process /usr/bin/dpkg returned an error code (1)
Some errors occurred while unpacking. I'm going to configure the
packages that were installed. ..................................

Setting up devscripts (2.5.8.1) ...
chown: root.root: invalid group
dpkg: error processing devscripts (--configure):
 subprocess post-installation script returned error exit status 1
Errors were encountered while processing:
 devscripts

installation script returned error exit status 100.
.............................................................................................................................................................................
I came across the same problem while unpacking lprng
What does it mean and how can I fix it?
Ciao
Vittorio