pbespgsolve: 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/pbespgsolve - from package: mcrl2

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

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