mrtg-load: 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/mrtg-load - from package: mrtgutils

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

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