x0vnc4server: 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/x0vnc4server - from package: vnc4server

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

Error in other languages:
x0vnc4server: bevel nie gevind nie
x0vnc4server: comandă negăsită
x0vnc4server: comando não encontrado
x0vnc4server: commande introuvable
x0vnc4server: command not found
x0vnc4server: käsku ei ole
x0vnc4server: không tìm thấy lệnh
x0vnc4server: komanda nerasta
x0vnc4server: Kommando nicht gefunden.
x0vnc4server: kommandot finns inte
x0vnc4server: komut yok
x0vnc4server: nie znaleziono polecenia
x0vnc4server: níor aimsíodh an t-ordú
x0vnc4server: no se encontró la orden
x0vnc4server: no s'ha trobat l'ordre
x0vnc4server: opdracht niet gevonden
x0vnc4server: parancs nem található
x0vnc4server: perintah tidak ditemukan
x0vnc4server: príkaz nenájdený
x0vnc4server: příkaz nenalezen
x0vnc4server: команда не найдена
x0vnc4server: командата не е открита
x0vnc4server: 命令找不到
x0vnc4server: コマンドが見つかりません