lock_screen_watcher: 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/lib/plainbox-providers-1/checkbox/bin/lock_screen_watcher - from package: plainbox-provider-checkbox

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

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