rsbackup.cron: 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/rsbackup.cron - from package: rsbackup

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

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