mssh: 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/bin/mssh - from package: mssh

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

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