pbesrewr: 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/pbesrewr - from package: mcrl2

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

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