vpnc-disconnect: 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/vpnc-disconnect - from package: vpnc-consoleuser
/usr/sbin/vpnc-disconnect - from package: vpnc

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

On Debian possible default full paths are:

/usr/sbin/vpnc-disconnect - from package: vpnc

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

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