stub_package_list: 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

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/lib/python3/dist-packages/plainbox/impl/providers/stubbox/bin/stub_package_list - from package: python3-plainbox

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