mono-server4-admin: 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-server4-admin - from package: mono-apache-server4

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

Error in other languages:
mono-server4-admin: bevel nie gevind nie
mono-server4-admin: comandă negăsită
mono-server4-admin: comando não encontrado
mono-server4-admin: commande introuvable
mono-server4-admin: command not found
mono-server4-admin: käsku ei ole
mono-server4-admin: không tìm thấy lệnh
mono-server4-admin: komanda nerasta
mono-server4-admin: Kommando nicht gefunden.
mono-server4-admin: kommandot finns inte
mono-server4-admin: komut yok
mono-server4-admin: nie znaleziono polecenia
mono-server4-admin: níor aimsíodh an t-ordú
mono-server4-admin: no se encontró la orden
mono-server4-admin: no s'ha trobat l'ordre
mono-server4-admin: opdracht niet gevonden
mono-server4-admin: parancs nem található
mono-server4-admin: perintah tidak ditemukan
mono-server4-admin: príkaz nenájdený
mono-server4-admin: příkaz nenalezen
mono-server4-admin: команда не найдена
mono-server4-admin: командата не е открита
mono-server4-admin: 命令找不到
mono-server4-admin: コマンドが見つかりません