mono-csc: command not found

Have You tried accessing the binary with the full path?

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/mono-csc - from package: mono-devel

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