backup-checkallused: 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/backup-checkallused - from package: chiark-backup

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

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