RESOLUTION
This can be done using the following commands when logged in as root via SSH on the Plesk server:
Linux Plesk versions:
# /etc/rc.d/init.d/psa stopall
# /etc/rc.d/init.d/psa start
FreeBSD Plesk, versions prior 8.1:
# /usr/local/psa/rc.d/psa stop
# /usr/local/psa/rc.d/psa start
FreeBSD Plesk since 8.1 version:
# /usr/local/etc/rc.d/psa.sh stop
# /usr/local/etc/rc.d/psa.sh start