After updating to version 2.3 the skript /etc/network/firewall.sh should be effected. This script refreshes the firewall rules and adds rules for the recently installed SSH login blocker. In case of automatic updates, this script will not take effect. Thus the cronjob, which is responsible for rereleasing the blocked IP addresses can not find the new line of rules. Please simply execute the script /etc/network/firewall.sh on the console or click the button "Save" in one of the overview pages of the firewall module. This also causes the execution of the script. Afterwards the cronjob can be effected correctly and therefore no more e-mails with this error message will be sent.