gnome-ppp: 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/gnome-ppp - from package: gnome-ppp

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

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