dntask: 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/dntask - from package: dnet-progs

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

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