mount.aptfs: command not found

Have You tried accessing the binary with the full path?

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:

/sbin/mount.aptfs - from package: aptfs
/usr/bin/mount.aptfs - from package: aptfs

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