A client got an email this morning with the following content from the Plesk cron daemon :
/usr/local/psa/libexec/modules/watchdog/cp/send-report weekly
PHP Fatal error: Class 'OptionalServices_ServicesConfiguration' not found
in /usr/local/psa/admin/plib/common_func.php3 on line 2948
Apparently, Plesk already released a fix for this and the fix can be seen at http://kb.parallels.com/en/9329. The thing is, the attachment is double-zipped so here's how you'd apply the fix :
gunzip send-report.gz
mv send-report send-report.gz
gunzip send-report.gz
cp /usr/local/psa/libexec/modules/watchdog/cp/send-report /usr/local/psa/libexec/modules/watchdog/cp/send-report.backup
mv send-report /usr/local/psa/libexec/modules/watchdog/cp/send-report
chmod 754 /usr/local/psa/libexec/modules/watchdog/cp/send-report
Good luck 