gnome-network-properties: 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/gnome-network-properties - from package: control-center

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

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