lpsxsim: 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/lpsxsim - from package: mcrl2

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

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