I am seeing these errors more frequently in the fail2ban.log This is a new setup - Ubuntu 8.04. No LAMP stack installed.

fail2ban.actions.action: ERROR iptables -n -L INPUT | grep -q fail2ban-ssh returned 100

fail2ban.actions.action: CRITICAL Unable to restore environment

I think I found part of the problem. It didn't look like IPTABLES was installed. Is it not installed as part of the package in Ubuntu 8.04?

when I issued the command iptables -L

I got back:
-bash: iptables: command not found

I ran:
apt-get install iptables

Then restarted Fail2Ban - I'll see if that clears up my fail2ban.log

It's recommended, not required:

http://packages.ubuntu.com/hardy/fail2ban

It looks like it was required in dapper (7.10), but changed to recommended in 8.04 and all later releases.

Thanks Guspaz. It (iptables) eliminated the errors I was seeing in the log for fail2ban.