cron-apt: 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/cron-apt - from package: cron-apt

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

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