on ispconfig.vhost file the custom_log directive is already commented out.
there is an ispconfig.conf file with
CustomLog "| /usr/local/ispconfig/server/scripts/vlogger -s access.log -t \"%Y%m%d-access.log\" -d \"/etc/vlogger-dbi.conf\" /var/log/ispconfig/httpd" combined_ispconfig
maybe you was referring to this file?
should i also comment out this?