dvdnav-config: 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/dvdnav-config - from package: libdvdnav-devel

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

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