Uninstall Dr Web:
# rpm -qa drweb | xargs rpm -e
Install the Dr Web packages:
# rpm -Uvh drweb-4.31.7-rh1.i586.rpm drweb-qmail-4.32-fc1.build71040907.02.i586.rpm
Recreate the qmail configuration files (important):
# /usr/local/psa/admin/sbin/mchk -v
An alternative could also be dropping Dr Web for the cheaper alternative Clean Server from 4PSA.
At the time of writing, Plesk had been updated to the latest available version (7.1.3)