nrpe: command not found

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 CentOS possible default full paths are:

/usr/sbin/nrpe - from package: nrpe

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/sbin/nrpe - from package: nagios-nrpe-server

You may install the required package with command apt-get install {package}

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