Thanks, I found the reason :-)
You must change the cron setting to run the script each minute. Edit /opt/etc/crontab and change setting from "*/5" to "*/1"
Code:Old setting:
*/5 * * * * admin nice /opt/bin/rrdtool.sh >> /opt/var/log/rrdtool.log 2>&1
New setting:
*/1 * * * * admin nice /opt/bin/rrdtool.sh >> /opt/var/log/rrdtool.log 2>&1

