ntdpal: 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/ntdpal - from package: primer3

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

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