First of all thanks again Till for trying to help me out.
The last sugestion didn't work also so again I am stuck.
Can't I point to the script directly for example
*/10 * * * * /usr/bin/lynx --dump /var/www/web4/web/scripts/admin/cronjobs.php > /dev/null
I also noticed that in the example cron from the script the "&" isn't there at the end. In the cronjobs from ISPConfig there is an "&".