mini_epn_nagios3: command not found

Have You tried accessing the binary with the full path?

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On Debian possible default full paths are:

/usr/bin/mini_epn_nagios3 - from package: nagios3-dbg

You may install the required package with command apt-get install {package}
Error in other languages:
mini_epn_nagios3: bevel nie gevind nie
mini_epn_nagios3: comandă negăsită
mini_epn_nagios3: comando não encontrado
mini_epn_nagios3: commande introuvable
mini_epn_nagios3: command not found
mini_epn_nagios3: käsku ei ole
mini_epn_nagios3: không tìm thấy lệnh
mini_epn_nagios3: komanda nerasta
mini_epn_nagios3: Kommando nicht gefunden.
mini_epn_nagios3: kommandot finns inte
mini_epn_nagios3: komut yok
mini_epn_nagios3: nie znaleziono polecenia
mini_epn_nagios3: níor aimsíodh an t-ordú
mini_epn_nagios3: no se encontró la orden
mini_epn_nagios3: no s'ha trobat l'ordre
mini_epn_nagios3: opdracht niet gevonden
mini_epn_nagios3: parancs nem található
mini_epn_nagios3: perintah tidak ditemukan
mini_epn_nagios3: príkaz nenájdený
mini_epn_nagios3: příkaz nenalezen
mini_epn_nagios3: команда не найдена
mini_epn_nagios3: командата не е открита
mini_epn_nagios3: 命令找不到
mini_epn_nagios3: コマンドが見つかりません