mcrl2xi: 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/mcrl2xi - from package: mcrl2

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

Error in other languages:
mcrl2xi: bevel nie gevind nie
mcrl2xi: comandă negăsită
mcrl2xi: comando não encontrado
mcrl2xi: commande introuvable
mcrl2xi: command not found
mcrl2xi: käsku ei ole
mcrl2xi: không tìm thấy lệnh
mcrl2xi: komanda nerasta
mcrl2xi: Kommando nicht gefunden.
mcrl2xi: kommandot finns inte
mcrl2xi: komut yok
mcrl2xi: nie znaleziono polecenia
mcrl2xi: níor aimsíodh an t-ordú
mcrl2xi: no se encontró la orden
mcrl2xi: no s'ha trobat l'ordre
mcrl2xi: opdracht niet gevonden
mcrl2xi: parancs nem található
mcrl2xi: perintah tidak ditemukan
mcrl2xi: príkaz nenájdený
mcrl2xi: příkaz nenalezen
mcrl2xi: команда не найдена
mcrl2xi: командата не е открита
mcrl2xi: 命令找不到
mcrl2xi: コマンドが見つかりません