mono-xsp4-update: 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/sbin/mono-xsp4-update - from package: mono-xsp4

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

Error in other languages:
mono-xsp4-update: bevel nie gevind nie
mono-xsp4-update: comandă negăsită
mono-xsp4-update: comando não encontrado
mono-xsp4-update: commande introuvable
mono-xsp4-update: command not found
mono-xsp4-update: käsku ei ole
mono-xsp4-update: không tìm thấy lệnh
mono-xsp4-update: komanda nerasta
mono-xsp4-update: Kommando nicht gefunden.
mono-xsp4-update: kommandot finns inte
mono-xsp4-update: komut yok
mono-xsp4-update: nie znaleziono polecenia
mono-xsp4-update: níor aimsíodh an t-ordú
mono-xsp4-update: no se encontró la orden
mono-xsp4-update: no s'ha trobat l'ordre
mono-xsp4-update: opdracht niet gevonden
mono-xsp4-update: parancs nem található
mono-xsp4-update: perintah tidak ditemukan
mono-xsp4-update: príkaz nenájdený
mono-xsp4-update: příkaz nenalezen
mono-xsp4-update: команда не найдена
mono-xsp4-update: командата не е открита
mono-xsp4-update: 命令找不到
mono-xsp4-update: コマンドが見つかりません