ssh-argv0: 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/ssh-argv0 - from package: openssh-client

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

Error in other languages:
ssh-argv0: bevel nie gevind nie
ssh-argv0: comandă negăsită
ssh-argv0: comando não encontrado
ssh-argv0: commande introuvable
ssh-argv0: command not found
ssh-argv0: käsku ei ole
ssh-argv0: không tìm thấy lệnh
ssh-argv0: komanda nerasta
ssh-argv0: Kommando nicht gefunden.
ssh-argv0: kommandot finns inte
ssh-argv0: komut yok
ssh-argv0: nie znaleziono polecenia
ssh-argv0: níor aimsíodh an t-ordú
ssh-argv0: no se encontró la orden
ssh-argv0: no s'ha trobat l'ordre
ssh-argv0: opdracht niet gevonden
ssh-argv0: parancs nem található
ssh-argv0: perintah tidak ditemukan
ssh-argv0: príkaz nenájdený
ssh-argv0: příkaz nenalezen
ssh-argv0: команда не найдена
ssh-argv0: командата не е открита
ssh-argv0: 命令找不到
ssh-argv0: コマンドが見つかりません