pbes2bes: 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/pbes2bes - from package: mcrl2

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

Error in other languages:
pbes2bes: bevel nie gevind nie
pbes2bes: comandă negăsită
pbes2bes: comando não encontrado
pbes2bes: commande introuvable
pbes2bes: command not found
pbes2bes: käsku ei ole
pbes2bes: không tìm thấy lệnh
pbes2bes: komanda nerasta
pbes2bes: Kommando nicht gefunden.
pbes2bes: kommandot finns inte
pbes2bes: komut yok
pbes2bes: nie znaleziono polecenia
pbes2bes: níor aimsíodh an t-ordú
pbes2bes: no se encontró la orden
pbes2bes: no s'ha trobat l'ordre
pbes2bes: opdracht niet gevonden
pbes2bes: parancs nem található
pbes2bes: perintah tidak ditemukan
pbes2bes: príkaz nenájdený
pbes2bes: příkaz nenalezen
pbes2bes: команда не найдена
pbes2bes: командата не е открита
pbes2bes: 命令找不到
pbes2bes: コマンドが見つかりません