Just to add
I followed this in the manual:
4) If this still doesn't help, then go to the command line of the server on which the error happens (on multiserver
systems, it is often the slave and not the master) and run (as root):
Comment out the server.sh cron job:
#* * * * * /usr/local/ispconfig/server/server.sh > /dev/null 2>> /var/log/ispconfig/cron.log
Then run the command:
Nothing logs on the command line.