Comment 2 for bug 414299

The root cause seems to be rkhunter failing to upgrade:

Log started: 2009-08-15 23:32:57
(Reading database ... 201407 files and directories currently installed.)
Preparing to replace kscreensaver 4:3.5.10-0ubuntu1~hardy1 (using .../kscreensaver_4%3a4.2.2-0ubuntu1_i386.deb) ...
Unpacking replacement kscreensaver ...
Processing triggers for man-db ...
Setting up rkhunter (1.3.2-6ubuntu1) ...
Updating the file properties database:
Database directory does not exist: /var/lib/rkhunter/db/mysql
dpkg: error processing rkhunter (--configure):
 subprocess post-installation script returned error exit status 1

Log started: 2009-08-15 23:33:58
dpkg: error processing kscreensaver (--configure):
 package kscreensaver is already installed and configured
Setting up rkhunter (1.3.2-6ubuntu1) ...