monop2: 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 CentOS possible default full paths are:

/usr/bin/monop2 - from package: mono-devel

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/bin/monop2 - from package: mono-devel

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

Error in other languages:
monop2: bevel nie gevind nie
monop2: comandă negăsită
monop2: comando não encontrado
monop2: commande introuvable
monop2: command not found
monop2: käsku ei ole
monop2: không tìm thấy lệnh
monop2: komanda nerasta
monop2: Kommando nicht gefunden.
monop2: kommandot finns inte
monop2: komut yok
monop2: nie znaleziono polecenia
monop2: níor aimsíodh an t-ordú
monop2: no se encontró la orden
monop2: no s'ha trobat l'ordre
monop2: opdracht niet gevonden
monop2: parancs nem található
monop2: perintah tidak ditemukan
monop2: príkaz nenájdený
monop2: příkaz nenalezen
monop2: команда не найдена
monop2: командата не е открита
monop2: 命令找不到
monop2: コマンドが見つかりません