pbesconstelm: 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/pbesconstelm - from package: mcrl2

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

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