mrtg-ip-acct: 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-ip-acct - from package: mrtgutils

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

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