Lighttpd

I got this error at the installation:

sudo apt-get install lighttpd
Reading package lists... Done
Building dependency tree       
Reading state information... Done
The following extra packages will be installed:
  libterm-readkey-perl libterm-readline-perl-perl spawn-fcgi
Suggested packages:
  rrdtool apache2-utils
The following NEW packages will be installed:
  libterm-readkey-perl libterm-readline-perl-perl lighttpd spawn-fcgi
0 upgraded, 4 newly installed, 0 to remove and 0 not upgraded.
Need to get 382 kB of archives.
After this operation, 1,331 kB of additional disk space will be used.
Do you want to continue [Y/n]? y
Get:1 http://ftp.uk.debian.org/debian/ squeeze/main libterm-readkey-perl armel 2.30-4 [33.6 kB]
Get:2 http://ftp.uk.debian.org/debian/ squeeze/main libterm-readline-perl-perl all 1.0303-1 [51.9 kB]
Get:3 http://ftp.uk.debian.org/debian/ squeeze/main lighttpd armel 1.4.28-2+squeeze1 [284 kB]
Get:4 http://ftp.uk.debian.org/debian/ squeeze/main spawn-fcgi armel 1.6.3-1 [12.8 kB]
Fetched 382 kB in 0s (590 kB/s)  
Selecting previously deselected package libterm-readkey-perl.
(Reading database ... 50154 files and directories currently installed.)
Unpacking libterm-readkey-perl (from .../libterm-readkey-perl_2.30-4_armel.deb) ...
Selecting previously deselected package libterm-readline-perl-perl.
Unpacking libterm-readline-perl-perl (from .../libterm-readline-perl-perl_1.0303-1_all.deb) ...
Selecting previously deselected package lighttpd.
Unpacking lighttpd (from .../lighttpd_1.4.28-2+squeeze1_armel.deb) ...
Selecting previously deselected package spawn-fcgi.
Unpacking spawn-fcgi (from .../spawn-fcgi_1.6.3-1_armel.deb) ...
Processing triggers for man-db ...
Setting up libterm-readkey-perl (2.30-4) ...
Setting up libterm-readline-perl-perl (1.0303-1) ...
Setting up lighttpd (1.4.28-2+squeeze1) ...
chown: invalid group: `www-data:www-data'
dpkg: error processing lighttpd (--configure):
 subprocess installed post-installation script returned error exit status 1
configured to not write apport reports
                                      Setting up spawn-fcgi (1.6.3-1) ...
update-alternatives: using /usr/bin/spawn-fcgi.standalone to provide /usr/bin/spawn-fcgi (spawn-fcgi) in auto mode.
update-alternatives: warning: not replacing /usr/share/man/man1/spawn-fcgi.1.gz with a link.
Errors were encountered while processing:
 lighttpd
E: Sub-process /usr/bin/dpkg returned an error code (1)

Then I wanted to set up a test page following the instructions for the 5 minute setup http://redmine.lighttpd.net/projects/lighttpd/wiki/TutorialConfiguration
and when I enter 127.0.0.1:3000 in the web browser I get an error page 404 - Not found.