mate-users-admin: 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-users-admin - from package: mate-system-tools

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

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