arpsend: 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 Debian possible default full paths are:

/usr/sbin/arpsend - from package: vzctl

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

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