fastcgi-mono-server4: 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/fastcgi-mono-server4 - from package: mono-fastcgi-server4

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

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