dupvserver: 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/dupvserver - from package: vserver-debiantools

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

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