plasma-windowed: 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/plasma-windowed - from package: kde-workspace-bin

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

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