The Webalizer package in Debian 6 has currently small bug as the required package for the GeoIP database is not installed automatically when Webalizer is installed. The symptoms are that Webalizer statistics was not created and this error message is displayed when Webalizer is run:
Error Opening file /usr/share/GeoIP/GeoIP.dat
The solution is to install the missing package manually:
apt-get install geoip-database