nm-applet: 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/nm-applet - from package: NetworkManager-gnome

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

On Debian possible default full paths are:

/usr/bin/nm-applet - from package: network-manager-gnome

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

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