nntpgrab_server: command not found

Have You tried accessing the binary with the full path?

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_server - from package: nntpgrab-server

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