I have this exact error in CentOS 5.3 x86_64, using ISPConfig 18.104.22.168:
FS#588 - CentOS: Monitoring plugin doesn't recognize fail2ban
I followed the The Perfect Server - CentOS 5.3 x86_64 [ISPConfig 3]
to the letter (and found another bug in it - you must run "yum install apr-devel" or you will fail compiling SuPHP).
Everything seems to be fine (still checking some functions), yet the fail2ban plugin isn't working.