apt-dater: 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/apt-dater - from package: apt-dater

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

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