massagevendor: 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/massagevendor - from package: arpwatch

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

On Debian possible default full paths are:

/usr/sbin/massagevendor - from package: arpwatch

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

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