pcnet-diag: 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/sbin/pcnet-diag - from package: nictools-pci

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

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