1 - What's your OMV version ? (dpkg -l | grep openmediavault)
2 - What's your openmediavault-fail2ban version ? (dpkg -l | grep openmediavault-fail2ban)
3 - I think fail2ban is started but you have error in log. Can you check fail2ban service is started ? ( ps -ef | grep fail2ban or service fail2ban status )
4 - I think a file is missing ...
5 - Have you test to desinstall and reinstall ? (force desinstall in hopeless case : dpkg -P openmediavault-fail2ban)
6 - With infos on 1,2,3 i can help you fully