pbes2bool: 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/pbes2bool - from package: mcrl2

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

Error in other languages:
pbes2bool: bevel nie gevind nie
pbes2bool: comandă negăsită
pbes2bool: comando não encontrado
pbes2bool: commande introuvable
pbes2bool: command not found
pbes2bool: käsku ei ole
pbes2bool: không tìm thấy lệnh
pbes2bool: komanda nerasta
pbes2bool: Kommando nicht gefunden.
pbes2bool: kommandot finns inte
pbes2bool: komut yok
pbes2bool: nie znaleziono polecenia
pbes2bool: níor aimsíodh an t-ordú
pbes2bool: no se encontró la orden
pbes2bool: no s'ha trobat l'ordre
pbes2bool: opdracht niet gevonden
pbes2bool: parancs nem található
pbes2bool: perintah tidak ditemukan
pbes2bool: príkaz nenájdený
pbes2bool: příkaz nenalezen
pbes2bool: команда не найдена
pbes2bool: командата не е открита
pbes2bool: 命令找不到
pbes2bool: コマンドが見つかりません