./masterpop3

Solution for Ubuntu 9.04

#aptitude install python2.5

Change the python version there execute the fail2ban-server script.
#vim /usr/bin/fail2ban-server

Change the first line from:
#!/usr/bin/python
–> to
#!/usr/bin/python2.5

After that restart fail2ban
# /etc/init.d/fail2ban restart

~# tail -f /var/log/fail2ban.log
2009-07-27 15:07:03,144 fail2ban.jail   : INFO   Jail ’ssh’ stopped
2009-07-27 15:07:03,627 fail2ban.server : INFO   Changed logging target to /var/log/fail2ban.log for Fail2ban v0.8.3
2009-07-27 15:07:03,628 fail2ban.jail   : INFO   Creating new jail ’ssh’
2009-07-27 15:07:03,628 fail2ban.jail   : INFO   Jail ’ssh’ uses poller
2009-07-27 15:07:03,651 fail2ban.filter : INFO   Added logfile = /var/log/auth.log
2009-07-27 15:07:03,652 fail2ban.filter : INFO   Set maxRetry = 6
2009-07-27 15:07:03,655 fail2ban.filter : INFO   Set findtime = 600
2009-07-27 15:07:03,656 fail2ban.actions: INFO   Set banTime = 3600
2009-07-27 15:07:03,812 fail2ban.jail   : INFO   Jail ’ssh’ started

Thanx to dudez at howtoforge.com