I've done a brand new install of ISPConfig 2.2.36 after following completly the perfect setup for my debian 5 lenny distro and had the same problem.
aptitude install liblwpx-paranoidagent-perl
apt-get install liblwpx-paranoidagent-perl
Should be missing or in the installation script or in the perfect setup
Then I've done:
After doing those commands my spamassassin is filtering now correctly.
Thank you for everything and for your very good work on ISPConfig