I'd previously blogged about the use of DCC, Pyzor and Razor and suggested puting the LoadModule directive in /etc/spamassassin/local.cf
Well, on review of /var/log/messages I found that SpamGuardian (Plesk) creates a link from /var/qmail/mailnames/user_prefs to the local.cf SA file. Because it uses this every time spamd runs, it doesn't like the administrative directives and creates a whole host of logged errors.
The LoadModule directives should be put in v310pre.cf and v312pre.cf instead. Check that everything still works with a spamassassin --lint and by checking in the logs.