Resolution
Check /usr/local/psa/var/log/maillog for possible errors. If you see something like:/var/qmail/mailnames/domain.com/mailuser/.spamassassin/user_prefs
Sep 17 11:29:51 vdnt spamd[7207]: bayes: cannot open bayes databases /var/qmail/mailnames/domain.com/mailuser/.spamassassin/bayes_* R/O: tie failed:It is the problem with the SpamAssassin Berkley database. Try to fix it according the information from the SA wiki page: http://wiki.apache.org/spamassassin/DbDumpAndLoad