Plesk is not accessible:
FATAL ERROR: Can not open log file '/var/log/sso/sso.log' (CWD is /usr/local/sso)
sso.log file is missing or incorrect permissions are assigned to it.
If the file does not exist, create it:
# touch /var/log/sso/sso.log
Set the following owner and file permissions to it:
# chown sso:root /var/log/sso
# chmod 777 /var/log/sso