Frontpage forms don't work and a site cannot be accessed using Frontpage client. The following errors appear in the domain's log $HTTPD_VHOSTS_D/domain.tld/statistics/logs/error_log: "Premature end of script headers: fpexe"
Plesk 'suexec' binary was replaced with another one.
Restore Plesk 'suexec' with the following command:
# cp -rp $PRODUCT_ROOT_D/suexec/psa-suexec /usr/sbin/suexec