dpns-ping: 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/bin/dpns-ping - from package: dpm

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

On Debian possible default full paths are:

/usr/bin/dpns-ping - from package: dpm

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

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