mate-panel: 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/mate-panel - from package: mate-panel

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

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