ssed: command not found

Have You tried accessing the binary with the full path?

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH

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/ssed - from package: ssed

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