lpssumelm: 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/lpssumelm - from package: mcrl2

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

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