nntpgrab_gui: 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 CentOS possible default full paths are:

/usr/bin/nntpgrab_gui - from package: nntpgrab-gui

You may install the required package with command yum install {package}

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