RoundCube webmail is accessed on an ISPConfig Nginx web server through the apps vhost. The PHP-FPM of the apps vhost is running under the user and group ispapps. To fix the above error you’ll have to change the owner of some RoundCube files.
Run these commands as root user to apply the changes.
chown root:ispapps /etc/roundcube/debian-db.php chmod 640 /etc/roundcube/debian-db.php chown root:ispapps /etc/roundcube/config.inc.php chmod 640 /etc/roundcube/config.inc.php chown -R ispapps:adm /var/log/roundcube chmod -R 750 /var/log/roundcube chown -R ispapps:ispapps /var/lib/roundcube/temp chmod -R 750 /var/lib/roundcube/temp
