lxlock: 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/lxlock - from package: lxsession

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

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